Agar (engine) – A high-level graphical application framework used by 2D and 3D computer games
Allegro library – A free crossplatform C/C++ game programming library, provides functions for graphics, sounds, input, timers, fixed and floating point, 3d, compressed datafile and a GUI.
APOCALYX 3D Engine – A free LGPL game engine based on OpenGL and several open source libraries.
Axiom Engine – A fork containing the core of the OGRE graphics engine written in C#
Game Blender – flexible node based game logic engine blender 3d
Boom – A port of the Doom source code by TeamTNT
ClanLib – A free cross-platform (including Mac OS X), object-oriented C++ game programming library.
Crystal Entity Layer – An extension of the Crystal Space 3D Engine
Crystal Space – A general framework for developing 3D applications
Cube – Powers the computer game of the same name
DarkPlaces – Heavily modified version of quake engine which supports modern graphics
Delta3d – Integrates other well-known free software projects into an easy-to-use API, originally developed by the U.S. Navy
Doom engine – The now free software engine originally used for the hugely popular Doom and Doom II
DXFramework – A simple, pedagogical 2D/3D DirectX-based game engine for Visual Studio
Eternity Engine – A source port of the Doom engine
Exult – A free software reimplementation of the Ultima VII game engine
FIFE – A free software 2.5D isometric game engine.
GZDoom – A source port of the Doom engine based on ZDoom
GemRB – A free software implementation of the Infinity Engine
Genesis3D – A real-time 3D engine for Windows
Genesis Device Is a powerful LGPL engine
id Tech 2 – Formerly known as the Quake II engine, the original open-source engine from id Software
id Tech 3 – Formerly known as the Quake III engine, the original open-source engine from id Software
ioquake3 – An updated fork of the GPL'ed id Tech 3 engine
Irrlicht Engine – A cross-platform and lightweight three dimensional graphics engine.
jMonkeyEngine – An open-source, BSD licensed Java scenegraph engine.
Jogre – A Java based client/server game engine and API for online real time games such as chess, checkers, etc.
KallistiOS – A free, BSD licensed development library for the Sega Dreamcast, by Dan Potter.
Lightfeather 3D Engine - A cross-platform, zlib licensed, real-time 3D graphics engine.
Nebula Device – A realtime 3D game engine developed by German game studio Radon Labs.
OGE - Open Game Engine - A cross-platform open source engine combining the components used to make games.
OGRE Engine – A very popular object-oriented graphics rendering engine. Also called OGRE3D
ORX - A portable, lightweight and data-driven 2D-oriented game engine.
Panda3D – A relatively easy to use python-driven game engine made by Carnegie Mellon University. Disney uses it to produce some of their games.
PLIB – A game engine – includes 3D, Audio, Music, GUI, Window manager and is portable Linux/Windows/Mac OS X.
ProQuake – A modified Quake engine
Quake engine – The original open-source engine from id Software
RealmForge – An open-source game engine for the Microsoft .NET Framework, predecessor to Visual3D.NET.
Retribution Engine – A game engine to make first person shooter games
Sauerbraten – A upgraded engine forked from the Cube engine
Spring - a full 3D free/open source RTS game engine
Stratagus – A cross-platform real time strategy game engine