Open source clone of the Age of Empires II engine
Injectable LUA scripting system, SDK generator, live property editor
A .NET ascii/ansi console engine written in C# for MonoGame and XNA
Game engine to build text adventures.
a UCI chess engine
2D Game Engine
Multi-platform game engine similar to old Megaman with a stage editor
Open Source 3D Game Engine
TurboSphere is an easy to learn and powerful JS based game engine.
A truly extensible cross-platform game engine