Opensource crossplatform Fallout 2 game engine writen in C++ and SDL
a UCI chess engine
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
Vivid is a modern C++ 3D engine using OpenGL4+
Go 3D Game Engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
QQ Group:538722494,KSFramework = KEngine + SLua(or xLua)
2D Game Engine
mGSTEP port of the Cube game engine
Improved version of the X-Ray Engine, the game engine
A cross platform Lua based game engine
A 2D game engine and level editor
Cross-platform 2D and 3D game engine
KlayGE is a cross-platform open source game engine
A cross-platform 2D game engine
A fast, scalable, distributed game server engine/framework for C++
Opensource Game Studio
IGS Labs
Low-Level Game Engine for Retro Platforms
Free and Open Game Programming Language for Windows and GNU/Linux
Real-time RPG for PC/tablet/phone; multiple quests and random dungeons
Blueshift is a cross-platform 3D game engine implemented in C++