Beamer

One keyboard and one mouse or trackpad for a Mac and a Windows PC on the same network, in either direction.

Push the pointer off the edge of the screen and it carries on onto the other machine, the way it would onto a second monitor. Or double-tap a key. The clipboard comes with you, your shortcuts still work, and what you type never leaves your network.

Download

Free, with no account. Every installer is on the releases page.

Platform	Get it	Notes
macOS 13 or later, Apple silicon	Beamer-<version>.dmg	Signed and notarised by Apple. Not for Intel Macs
Windows 10 and 11	Beamer-Setup-<version>.exe	Not code-signed; see step 1 below
Windows, through winget	winget install KalkmanCode.Beamer	The same installer, without the warning

Quick start

1. Install on both machines. On the Mac, drag Beamer to Applications, open it, and press the two Grant buttons on the Permissions page (Accessibility, then Input Monitoring), then Relaunch Beamer on the same page: macOS only passes keys to an app started after the grant, so until then the pointer crosses but the keyboard does not. On Windows, run the installer. It is not code-signed, because a certificate costs money and Beamer is free, so Windows says "Windows protected your PC" the first time: choose More info, then Run anyway. winget does not show that warning. Beamer on Windows runs as administrator, so expect one UAC prompt when you open it.
2. Pair them. Both Overview pages lead with pairing until it is done. On the PC, press Pair a Mac; a six-digit code appears. On the Mac, choose the PC from the list and type the code. It lasts a minute and works once. If the PC never appears in the list, as on guest Wi-Fi or across a VPN, type the address the PC shows next to its code into "PC not listed?" on the Mac and press Find. The PC joins the list, and you pair with the code as before.
3. Cross. Push the Mac's pointer off the right-hand edge of its screen, or double-tap Right Option, and the Mac's keyboard and trackpad are on the PC. Push back through the PC's left edge, or double-tap again, to come home. The PC's own keyboard and mouse go the other way: push through the same edge, or double-tap Right Ctrl.

That is all most people need. The edge, the keys and everything else can be changed in each machine's settings.

Screenshots

In your own appearance: light if your GitHub is light, dark if it is dark.

Mac	Windows

What it does

• Push through the edge. Off the edge that faces the other machine, only along the parts of it you pick, through a corner, or up through the MacBook's notch. The pointer arrives at the same point along the border, on the right display however your monitors are stacked or staggered. The edge lights up as you push, and the trackpad ticks as the push builds.
• See where you land. A switch by the key or a menu plays a short arrival around the pointer on the machine that takes over, so you never hunt for it.
• Or press a key. Double-tap or hold a trigger key to switch without moving the pointer. Right Option on the Mac and Right Ctrl on the PC to start with; on either machine it can be any key that types nothing, recorded by pressing it.
• Either way round. The Mac drives the PC and the PC drives the Mac. Each machine has a switch per direction, so you can turn one way off and keep the other.
• The clipboard comes with you. Text and images, both ways, at the moment you switch. Files stay where they are.
• Your shortcuts still work. Cmd becomes Ctrl and Option becomes Alt on Windows, so Cmd+C copies there too. The PC gets the reverse: its Ctrl+C arrives on the Mac as Cmd+C. Either machine can switch to Positional instead, where each key arrives as the key in its place.
• Media keys follow you to the PC. While the Mac drives the PC, play, pause, skip, mute and volume act on the PC. Brightness stays with the Mac. The PC's own media keys do not reach the Mac yet.
• Keys and buttons that stay put. Each machine keeps a list of keys and mouse buttons that keep working where they were pressed while its input is on the other one: a mouse's back button for this machine's browser, a volume key for its speakers. Add one by pressing it. The back and forward side buttons cross in both directions otherwise.
• Mac gestures on Windows. Three or four fingers up for Task View, down for the desktop, left and right to change virtual desktop, all from the Mac's trackpad.
• Make it yours. Glow and Beam, or nine other effects in three families (Membrane, Sparks and Instrument), each with colour packs of its own and any colour with any effect. The notch as an outline or an island with a meter, how hard you push before it crosses, and settings windows that follow the system's light or dark appearance or keep your own choice.
• Feels like your own. Each machine sets how the other's pointer moves and scrolls on it, from 25% to 400%, and can reverse its scrolling, so a Mac trackpad and a PC mouse each feel right on the other screen.
• Out of the way when it should be. A full-screen app holds the edges, so a game or a film never loses the pointer; the trigger key still works. Pause crossing does the same by hand. A drag that reaches the edge stays a drag. Switch to a machine that is asleep and Beamer wakes it, where that machine answers wake-on-LAN: a PC usually does, a MacBook on Wi-Fi usually does not.
• Your network, nobody else's. No server in the middle. The two machines talk to each other directly, encrypted, and you pair them once with a six-digit code. The only thing that ever goes further is a once-a-day check of GitHub's public releases for a newer version, which you can switch off on Overview. More in SECURITY.md.
• Free and open source. No account, no subscription, GPL-3.0.

Settings

Each machine has its own settings window and makes its own choices about how input leaves it. Both sidebars end with the version and a link to kalkmancode.co.uk/beamer, and both menus have About Beamer.

Page	Mac	Windows
Overview	Pairing (first, until it is done), where input is, the link and its round trip, Send input and Pause crossing, a switch per direction, start at login, the update check	Pairing (first, until it is done), where input is, the link and its round trip, Send input and Pause crossing, a switch per direction, start at sign-in, the update check
Permissions	Accessibility and Input Monitoring, with Relaunch Beamer	None; the firewall check is on Connection
Crossing	A drawing of the arrangement, the ways in (edge, part of the edge, corner, notch), where the PC is, never while dragging, resistance, the shortcut	A drawing of the arrangement, the ways in (edge, part of the edge, corner), where your Mac is, never while dragging, resistance, the shortcut
Keyboard	Same shortcuts or same positions, what stays on this Mac, the PC's pointer and scroll speed here	Same shortcuts or same positions, what stays on this PC, the Mac's pointer and scroll speed here
Design	Crossing and switch styles, each playing as you point at it, colours, show where the pointer lands, notch style, trackpad ticks, the window's appearance (System, Light or Dark)	Crossing and switch styles, each playing as you point at it, at the edge or a corner, colours, show where the pointer lands, the window's appearance (System, Light or Dark)
Connection	Hide addresses, the PC's address, port and token	Whether Windows Firewall lets the Mac in, with a one-button fix; hide addresses; this PC's address, port and token

Which edge of the Mac leads to the PC is one setting either machine can change; the two keep it in step, so the border is always the same one seen from both ends.

Known limits

• The Windows secure desktop cannot be driven. UAC prompts, Ctrl+Alt+Del and the lock screen refuse input from any app by design, and Ctrl+Alt+Del cannot be sent at all. Use the PC's own keyboard there.
• Files do not cross, only text and images, up to 256KB of text and an 8MB image.
• AltGr is out of reach from the Mac.
• A dead key typed on the PC does not cross, so an accent typed as two keys on the PC's layout arrives on the Mac without it. Shortcuts and letters follow each machine's own layout.
• Intel Macs are not supported. The Mac app is built for Apple silicon only.
• The Windows installer is unsigned. SmartScreen warns until it has a download history; winget avoids it.
• macOS 27 beta 4 could block a signed app's local-network access even when Terminal could reach the PC. The released macOS 27 does not, so the DMG no longer carries a workaround; for that beta, mac_app/Beamer Tunnel.command in this repository forwards the link over SSH: open it, leave its window running, then open Beamer, which uses the tunnel only when its direct connection is blocked.

In detail

Connection states

Written from the Mac, which connects to the PC. The PC's link to the Mac reports the mirror of them, naming the Mac.

Status	Meaning
Connected to <address>:<port>	The encrypted link is up: the PC decrypted the Mac's first frame, so both hold the same token, and the protocol versions match. Reads Connected to Windows via secure macOS 27 fallback when the tunnel is carrying it.
Windows is reachable, but Beamer is not listening on this port.	The PC answered but nothing accepted the TCP port.
Windows could not be authenticated — check the shared token matches on both sides	The two derived different keys. The tokens differ.
Windows is unreachable from this Mac	Nothing got as far as Beamer or the firewall. Check Wi-Fi client isolation, the PC's network, and that the Mac can resolve its address.
Windows did not answer the handshake — it is probably running an older Beamer; update it	A PC that has never completed a handshake this run is silent, as a Beamer from before encryption is.
Windows receiver speaks Beamer protocol vN, this Mac vM — update both apps	The wire versions differ. The version travels in cleartext at the start of the connection, so a mismatch says so rather than hanging.
Windows stopped responding	No ping or acknowledgement for about two seconds.

Both ends notice a dead link within a few seconds. The PC enforces a 2.5-second read timeout and the Mac pings at least once a second while idle, so the PC is back to waiting for the Mac within about three seconds; the Mac notices in about two and takes its input back.

The Mac always fails open. A dropped connection, a missing acknowledgement, a crashed capture worker or a full event queue returns input to the Mac at once. A watchdog runs for as long as a socket exists, so a half-open connection is caught and the Mac reconnects even if you never switched. Trying to switch while the link is down beeps and posts a notification.

Crossing

Push the pointer at the outer edge and it does not move: the push builds as pressure, the edge lights up, the trackpad ticks at each quarter, and once you have pushed far enough the boundary gives. The resistance is the point. An edge that switches the instant you touch it does so every time you overshoot a close button. The default is 120 points; zero switches on contact.

Way in	Where it triggers	Mac	PC
Shortcut	Double-tap the trigger key, or hold it	Yes	Yes
Edge	The whole of one outer edge	Yes	Yes
Part of the edge	Only the thirds of that edge you pick (start, middle, end), measured on the display under the pointer	Yes	Yes
Corner	An 8pt box in one corner, needing a diagonal push	Yes	Yes
Notch	The top edge, only within the notch's width	Yes	No

Any combination can be on, except Edge and Part of the edge, which exclude each other. On the Mac, shortcut and the right-hand edge are on to start with.

• The notch has no pixels to light, so a push there draws on the notch itself. Outline, the default, runs a comet of light round a small tab under the notch that brightens and speeds up with the push. Island springs a black island out of the notch with a four-segment meter; with Reduce Motion on it stays one size and fades with the push.
• An edge counts wherever no display of the same machine lies beyond it, so an edge between two displays behaves as the system intends, and the edge of a MacBook under a wider external display still crosses.
• The pointer arrives where it left: 42% of the way down the Mac's right edge is 42% of the way down the PC's left edge, on whichever monitor owns it.
• Crossing never fires while a mouse button is held, because a drag that reaches the edge is a drag.
• It suspends itself while a full-screen app has focus. Pause crossing in the Mac's menu bar puts it away until you resume it or restart Beamer.
• Only one machine's input is on the other at a time. While the Mac drives the PC, pushing the PC's own mouse through the edge sends the Mac's input home and takes the PC's mouse across behind it.
• Either machine's own switch, the menu item or the trigger key, sends the other's input home, so a way back never depends on the edge alone. The PC's edge facing the Mac leads home even when the Mac has only its shortcut on.
• Switching to a PC that is asleep sends wake-on-LAN. The PC's hardware address is read from the Mac's ARP table after a successful connection, never typed.

Each machine's menu has one tick per direction: This Mac drives Windows and Windows drives this Mac on the Mac, Mac drives this PC and This PC drives the Mac in the Windows tray. Turning one off stops that direction only.

Keys, buttons and media keys

Mac modifiers map to Windows by meaning, so the shortcuts your fingers know keep working. The Mac's Keyboard page can switch this to positional, where Cmd sends the Windows key.

Mac key	Sends on Windows
Cmd	Ctrl
Ctrl	Windows key
Option	Alt

So Cmd+C, Cmd+V, Cmd+Z and Cmd+T are copy, paste, undo and new tab, Ctrl+E opens Explorer and Ctrl on its own opens Start. The PC's keys arrive on the Mac the reverse way. Chords with Ctrl, Alt or Windows held are sent as real virtual-key presses, so they land on the right key for the active Windows keyboard layout. The Mac reads its own layout too, so on a German or French Mac Cmd+Z is still undo and Cmd+A still selects all, and a letter typed from the PC lands on the key that types it. When the two machines are on layouts of different alphabets, say the PC on Russian and the Mac on English, a letter types what the receiving machine's own layout has on that key, as its own keyboard would, and shortcuts keep working. The key_map object in each app's config JSON can still override single keys.

The trigger key is never forwarded. On both machines it is recorded by pressing it: Right Option on the Mac and Right Ctrl on the PC to start with. Either can double-tap or hold.

The stays-here list is per machine, because a Mac keycode and a Windows virtual key are different numbers for the same key. It takes keys, the right, middle, back and forward mouse buttons, and on the Mac its media keys. A listed press stays on the machine it was pressed on while input is away; its release goes wherever its press went, so nothing is ever left held down on the far side. The trigger key cannot be added.

The Mac's F7–F12 media row and volume keys forward to the PC as play/pause, next, previous, mute and volume. On the Mac they arrive as system events rather than key events and are captured separately (mac_app/media_keys.py). Brightness and keyboard-backlight keys stay with macOS, since Windows has no equivalent.

Ctrl+Alt+Del is the Secure Attention Sequence, trapped by the kernel before any app sees it. SendInput cannot produce it, and SendSAS() needs a Windows service or a signed uiAccess app installed under Program Files, which Beamer is not.

Gestures

Trackpad scrolling is smooth and horizontal scrolling works on Windows. While input is on the PC, the Mac's system gestures do the equivalent thing there and nothing on the Mac:

Mac gesture	On Windows
Three or four fingers up (Mission Control)	Task View
Three or four fingers down (App Exposé)	Show desktop
Three or four fingers left or right (Spaces)	Switch virtual desktop, the same way round
Thumb and three fingers spread (Show desktop)	Show desktop
Thumb and three fingers pinched (Launchpad)	Start
Two-finger pinch	Zoom (Ctrl+scroll)
Two-finger swipe between pages	Back and forward (Alt+Left/Right)

The Mac classifies a system gesture when it ends and sends one message. The PC replays it as a real swipe through a synthetic Precision Touchpad, so Windows' own touchpad settings apply and Task View animates as it would under fingers. Where Windows refuses that device, it presses the shortcut with the same default meaning instead (Win+Tab, Win+D, Win+Ctrl+Left/Right, Win). Direction comes from private macOS event fields, keyed by macOS major version in mac_app/gestures.py, because the horizontal sign has flipped between releases.

Clipboard

The clipboard moves at the moment of a switch, ahead of the switch itself: switching from the Mac carries the Mac's clipboard to the PC, and switching back carries the PC's to the Mac. Where it holds both an image and text, both cross and the pasting app picks. The caps keep the switch prompt: 256KB of text and an 8MB image as PNG. Over a cap, that half is left alone rather than truncated. The PC converts to and from the Windows clipboard's DIB format itself, using the Qt it already ships. A switch sends the clipboard only when it has changed since it last crossed, so a large image is not re-sent every time.

Latency

If both machines are on Wi-Fi, every event crosses the air twice, Mac to access point to PC. Ethernet on either machine removes a hop. Where Wi-Fi is unavoidable, 5GHz or 6GHz and turning off power saving on the PC's adapter both help.

Beamer sends every event at once (TCP_NODELAY). Acknowledgements are coalesced over 15ms so a 100Hz stream of moves cannot double the packet count, with an idle heartbeat every 400ms. The Mac's settings show the measured round trip while input is on the PC.

Security

Both apps derive a key from the shared token with HKDF-SHA256 and seal every frame with ChaCha20-Poly1305. The token is never sent. Pairing agrees a token with CPace, a password-authenticated key exchange over X25519, from the six-digit code, so nothing sent while pairing can be tested against a list of codes. What that does and does not protect against is in SECURITY.md.

Update check

Once a day, and at start, Beamer asks GitHub's public releases API for the latest release of this repository and compares its version with its own. A new minor or major version is always offered; a patch release (1.4.0 to 1.4.1) only when its release notes ask for it, so a run of small fixes does not nag. Drafts and pre-releases never count and nothing is downloaded. When a newer one is out, the menu says Beamer X is available and Overview offers a Download button that opens the release page. The request is an ordinary HTTPS request, so GitHub sees the address it came from, as it would for a browser. Switch it off with Check for updates on Overview.

Windows specifics

The installer puts Beamer in %LOCALAPPDATA%\Beamer for the current user with a Start menu shortcut. Quit Beamer from the tray before installing a newer version over it; only one instance runs at a time.

Beamer runs elevated (its exe carries a requireAdministrator manifest), because Windows silently drops input from a non-elevated app aimed at an elevated window such as an admin PowerShell. Start Beamer when you sign in, on Overview, writes and removes an elevated Beamer logon task; nothing else touches autostart.

Beamer needs two inbound rules on Private networks: TCP 24820 for input and UDP 24821 for pairing, both below the range Windows and macOS hand out for themselves. The app adds them on its first elevated start. Connection says in one sentence whether the Mac can get in and offers one button for whichever of three things usually stops it: the rule is missing (it adds it), Cancel was pressed on Windows' own "allow this app" prompt, which writes a block rule that beats any allow rule (it removes the block and adds the rule), or the network is classed as public (it marks the network private rather than opening the port on every public network).

The lock screen. No elevation lets an app type there: it is the Winlogon secure desktop, which admits only SYSTEM. On a PC with the author's separate unlock credential provider installed (not part of this repository), switching to a locked PC signals that provider, which unlocks it in about four seconds; input sent meanwhile is dropped. Beamer only signals the provider and never holds a password. Without it, the Mac reports Windows is locked — unlock it at the PC.

Building from source

On the Mac, double-click mac_app/Install-Beamer-Mac.command. It builds a self-contained app, installs it at /Applications/Beamer.app, and leaves it closed so the permission prompts do not appear unexpectedly.

On Windows, run win_app\Install-Beamer.ps1 from an admin PowerShell. It builds and installs %LOCALAPPDATA%\Beamer\Beamer.exe, adds a Start menu shortcut and the two firewall rules. From a non-admin PowerShell it still installs but skips the rules, which the app adds on its first elevated start.

Pairing is the easy path, not the only one: each Connection page still takes an address, port and shared token typed by hand, and they must match on both machines.

Development checks

From mac_app:

.venv/bin/python3 -m unittest discover -s tests -v
./build_dmg.sh

From win_app:

python -m unittest discover -s tests -v
.\build_win_app.ps1

A local Mac build is signed with the release's Developer ID identity when the login keychain can reach it, so privacy grants carry between local builds and releases, and ad-hoc otherwise (over SSH), under the hardened runtime either way. It is not notarised.

Files shared by both apps (receiver.py, return_edge.py, pairing.py, ignored.py, tokens.py and others) are byte-identical copies, because each app bundles only what sits under it; a test fails if a pair drifts. Beamer.svg is the master of the mark, and Beamer.ico, Beamer.png and Beamer.icns are rendered from it.

Release builds

The version lives once, in VERSION at the repository root; the Mac build number is the commit count. Change VERSION, commit, then build each platform from that commit. Both commands refuse uncommitted changes outside docs/, upload nothing except the Mac's notary submissions, and write to docs/beamer-releases/<version>/ in the folder that contains the repository.

On the Mac, from mac_app, in a desktop session (the keychain will not release a Developer ID identity over SSH):

./build_dmg.sh --release

It signs every nested binary with Developer ID under the hardened runtime with a secure timestamp, checks the bundle still runs, notarises and staples the app, then the DMG, and checks both with stapler validate and spctl. Notarisation uses the App Store Connect API key named in ~/.appstoreconnect/key_id.

On Windows, from win_app:

.\build_win_app.ps1 -Release

It runs the tests, builds Beamer.exe and compiles Beamer-Setup.iss with Inno Setup 6 into Beamer-Setup-<version>.exe. The installer adds no firewall rules and leaves autostart off.

Licence and support

GPL-3.0; see LICENSE. Releases up to and including 1.2.0 were MIT.

Beamer is free and made by one person. Issues are welcome and read, but there is no guarantee of a reply. Before a pull request, read CONTRIBUTING.md. Report security problems privately, as SECURITY.md describes. Home page: kalkmancode.co.uk/beamer.

A bug report is far easier to act on with each machine's log attached. Open log folder in each machine's menu opens it: ~/Library/Logs/Beamer/Beamer.log on the Mac and %LOCALAPPDATA%\Beamer\Beamer.log on Windows. They hold your machines' names and local network addresses, so look them over before posting.