Best open-source C# projects

A native macOS menubar app showing live upload and download speeds, router bandwidth, per-app traffic and built-in speed tests.

A free, open-source desktop file converter you use by dragging files onto a format wheel at the cursor, working offline across 240+ formats.

A free, open-source, local-first Windows desktop organizer that groups desktop files into folder-backed widgets alongside notes, todos, search, and weather.

Windows app for low-latency iPhone and iPad screen mirroring over USB or AirPlay, with D3D11 preview, multi-device sessions and OBS window capture.

An MCP server and CLI that let AI agents drive the real Microsoft Excel application on Windows through its COM API.

Free, open-source Windows optimization tool with 42 tweaks for performance, privacy, and debloating, plus built-in system management utilities.

A Windows screen recorder that captures a selected area, webcam, or sketchboard and exports the result as GIF, APNG, video, PSD, or PNG.