Gtk# is a Mono/.NET binding to the cross platform Gtk+ GUI toolkit and the foundation of most GUI apps built with Mono
Contains some simple and commonly used WPF controls
Cross-platform .NET/Mono bindings for LibVLC
Bindings to create MacOS X applications with Mono.
Audio and MIDI library for .NET
SkiaSharp is a cross-platform 2D graphics API for .NET platforms based on Google's Skia Graphics Library. It provides a comprehensive 2D API that can be used across mobile, server and desktop models to render images.
A cross-platform UI toolkit for creating desktop applications with .NET and Mono