A game engine powered by python and panda3d
Open source clone of the Age of Empires II engine
An OpenGL RTS game engine written in C
GemRB is a portable open-source implementation of the Infinity Engine
Haskell game engine library for roguelike dungeon crawlers
State Management and Multiplayer Networking for Turn-Based Games
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.