3D game engine/framework in C, with Luajit and Python bindings now
Full featured MUD server with all the trimmings.
Orx: Data-Driven Game Engine
A game engine for console based text games
Low-Level Game Engine for Retro Platforms
scriptable game engine with built-in support for 2D graphics and sound
A game engine written in the D programming language
A 3D, fully concurrent game engine