One framework for creating powerful cross-platform games
A game framework written with osu! in mind.
2D Game Engine
3D .NET engine for Windows, Linux, Mac
A cross-platform game framework based on OpenGL and GObject.
An open source skateboard games engine written in C# and .NET.
Open Source Virtual World and MMOG Development Platform
I am working on upgrading the XNA Platform Game Template.
Fully fledged steam community SDK