Lemon

A drag-and-drop file converter for Windows and macOS. Drop in pictures, audio, video or documents, pick a format for each file (or for all of them at once), and convert the whole batch in parallel. Or skip the window: while you drag files anywhere on your computer, shake the mouse and a wheel of formats pops up under the pointer. Drop on one and the converted copy appears next to the original.

Download: Releases page (Windows releases are tagged windows-v…, Mac releases mac-v…). On a Mac, also brew install --cask kataruna/tap/lemon. See the install guide.

Guide	What's in it
INSTALL.md	Installing, first steps, converters, updating and uninstalling, on Windows and Mac
DETAIL.md	How each part works: the wheel, the queue, every conversion, Optimize, Remove background, settings
BUILD.md	Building, testing, packaging and releasing both apps, and where the code lives

Features

• Conversion wheel. While you drag files from anywhere (File Explorer, Finder, the desktop, a browser…), shake the mouse or press a key (Alt on Windows, Control on Mac, or your own) and a round menu of formats opens under the pointer. You can also select files in File Explorer (hold Alt) or Finder (hold Control). Drop on a format to convert right away; drop on the lemon in the middle to add the files to the queue. Esc closes the wheel without cancelling the drag.
• Rings. The wheel has rings for Convert, Optimize, Cut out (remove the background) and Resize, plus up to five rings of your own. Switch with Tab, the number keys, the scroll wheel, or by resting the files on a ring's name. A hub can show all the rings at once.
• Commands. Your own shell (or PowerShell) commands on a Commands ring for dragged files, folders and links: shake a project folder to open it in your terminal or editor, or a link from the browser to hand it to your own tool. See DETAIL.md.
• Batch queue. Drop files or whole folders on the window, give each file its own preset (or use Set all to), and convert them in parallel with live progress.
• Optimize. Makes images, videos and PDFs smaller in the same format, with the quality kept close to the original, in three strengths: Lossless, Balanced and Smaller.
• Remove background. Cuts the subject out of a picture onto a transparent PNG, with the BiRefNet AI model running on your own computer (and Apple Vision on the Mac).
• Resize. Shrinks pictures to 4K, Full HD, HD or SD in the same format. It also upscales 2× or 4× with the Real-ESRGAN AI model running on your own computer.
• Presets. Dozens built in (WebP – Web optimized, MP3 – 320 kbps, MP4 – 720p small, Animated GIF…), and your own with quality, size, bitrate, CRF, frame rate and metadata settings.
• Make it yours. Themes (including your system's accent color), glass, the emoji in the middle, which formats go on the wheel, and which ring each kind of file opens on, all with a live preview.
• Welcome guide. On first launch, Lemon offers to install the free converters it uses (with winget on Windows, Homebrew on Mac) and shows how the wheel works.
• Update check. Lemon tells you when a newer version of your platform's app is on the Releases page. Nothing installs by itself, and nothing else is sent. It can be turned off in Settings › About.
• Safe output. Originals are never overwritten. A taken name becomes name (1).ext, and half-written files are removed when a conversion fails or is cancelled.

Windows and Mac

The two apps are written separately (C# / WinUI 3 and Swift / SwiftUI) and share no code, but they work the same way. The differences:

	Windows	Mac
Runs on	Windows 10 (2004+) and 11, 64-bit	macOS 14 Sonoma or later, Apple silicon
Lives in	The notification area (by the clock)	The menu bar
Wheel key by default	Alt (pressed mid-drag, or held over files selected in File Explorer)	Control (held mid-drag, or over files selected in Finder)
Pictures	Built in (bundled ImageMagick)	ImageMagick from Homebrew
Simple documents	Markdown and text built in	DOCX, ODT, RTF, HTML and text built in (textutil)
Remove background	BiRefNet on the GPU (DirectML) or CPU	Apple Vision, or BiRefNet on the CPU
AI upscale	Real-ESRGAN on the GPU (DirectML) or CPU	Real-ESRGAN on the GPU and Neural Engine (Core ML) or CPU
Right-click Convert with Lemon	Yes	Not yet
Packages	Installer and portable .exe	Lemon.app in a zip

Inspiration

Tangerine on macOS, whose drag-and-drop conversion (and hold-Shift gesture) Lemon started from, and Clop, which Optimize follows (its aggressive mode became Smaller).

How it was made

Lemon was developed with AI coding agents (Claude Code): the agents wrote the code, tests and docs. A human directed the work, designed the user experience, and tested the apps on real Windows and Mac machines.

Thanks

Lemon is a friendly front end on top of a lot of excellent free software. Thank you to everyone who builds and maintains these projects.

The converters that do the real work:

Project	What Lemon uses it for
ImageMagick	Pictures: every image format, Resize, and Optimize for JPEG, PNG, WebP and GIF (on Windows through Magick.NET, built in)
FFmpeg	Audio and video, and Optimize for videos
Pandoc	Documents and ebooks: DOCX, ODT, RTF, HTML, Markdown, EPUB
LibreOffice	Office files to PDF
Ghostscript	Optimize for PDFs

Remove background:

Project	What Lemon uses it for
BiRefNet	The AI model that cuts out the subject, in the ONNX versions published by ONNX Community (Lite, full)

Upscale:

Project	What Lemon uses it for
Real-ESRGAN	The AI models that enlarge pictures (realesr-general-x4v3 and RealESRGAN_x4plus, BSD 3-Clause, © 2021 Xintao Wang), exported to ONNX by windows/packaging/export-upscale-models.py
ONNX Runtime	Runs the model: with DirectML on Windows, and through the Swift package on Mac

Libraries and tools in the apps:

Project	What Lemon uses it for
Windows App SDK (WinUI 3)	The Windows app's interface
.NET Community Toolkit (MVVM)	View models in the Windows app
Markdig	Markdown to HTML on Windows, without Pandoc
xUnit	The Windows tests
Inno Setup	The Windows installer
winget and Homebrew	Installing the converters from the welcome guide

Issues

Report problems on the issue tracker. On Windows, %LOCALAPPDATA%\Lemon\errors.log is useful to attach.