The C# SDL-project is built in two parts: SDL.NET and C#-wrappers for SDL.
SDL.NET is a set of object-oriented CLS-compliant .NET bindings for the SDL gaming library and provides high-level access to audio, keyboard, mouse, joystick, TrueType fonts, various image formats, sound mixing, MPEG-1 movies, and 2D video framebuffer.
To build SDL.NET we use C#-wrappers around SDL and some other SDL-related libraries. The current release uses taosdl, but the plan is to make our own version of the wrapper.
See the documentation wiki for more details.