Cross-Platform C++ 2D/3D game engine
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
The Open Toolkit library is a fast, low-level C# wrapper for OpenGL
3D Procedural Game Engine Using OpenGL
2D game development library for Ruby and C++
A modern, cross-platform Quake game engine based on FitzQuake.
GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
An isometric arcade-style game of skill, puzzles and exploration
Pycraft is an open-source, OpenGL based game made in Python
Amateur 3D Game Engine
C++ lightweight cross-platform game engine
Vivid3D is an open-source 3D engine with powerful 2D UI.
Vivid is a modern C++ 3D engine using OpenGL4+
Go 3D Game Engine
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Opensource Game Studio
Blueshift is a cross-platform 3D game engine implemented in C++
Portable game engine with main focus on point-and-click adventures
3D Game Engine
A 3D game engine in java.
Mahasona engine is an open source game engine.