3D game engine/framework in C, with Luajit and Python bindings now
GemRB is a portable open-source implementation of the Infinity Engine
Orx: Portable Game Engine
A Tile-based Game Engine written in C# mimicing retro consoles.
A cross platform Lua based game engine
Low-Level Game Engine for Retro Platforms
Portable game engine with main focus on point-and-click adventures
scriptable game engine with built-in support for 2D graphics and sound
Multi-platform game engine similar to old Megaman with a stage editor
An advanced flexible game engine for Java.
A generic 2D engine for any kind of game
A 2D Adventure Game & Engine
A 3D, fully concurrent game engine
A truly extensible cross-platform game engine