Posting it here and will add links as I go.
Free Engines
Agar (engine) - A high-level graphical application framework used by 2D and 3D computer games http://libagar.org/
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. http://en.wikipedia.org/wiki/Allegro_library
Axiom Engine - A fork containing the core of the OGRE graphics engine http://axiomengine.sourceforge.net/wiki ... /Main_Page
Haaf's Game Engine - A 2D Hardware Accelerated Game Engine http://hge.relishgames.com/
Baja Engine - Professional quality engine used for the game The Lost Mansion. http://www.bajaengine.com/
Boom2 - A port of the Doom source code by TeamTNT http://www.geocities.com/SiliconValley/ ... /boom2.htm
Build engine - A First person shooter engine used to power Duke Nukem 3D http://en.wikipedia.org/wiki/Build_engine
Cadabra 3D Engine - 3D engine for easy game development http://www.cadabra3d.org/
Catmother - A BSD-licensed engine from a company that open-sourced its code when it closed the business. http://catmother.sourceforge.net/
CheapHack - An outdated TomazQuake derived engine http://www.moddb.com/mods/286/cheaphack
Crystal Entity Layer - An extension of the Crystal Space 3D Engine
Crystal Space - A general framework for developing 3D applications http://www.crystalspace3d.org/main/Main_Page
Cube - Powers the computer game of the same name http://cubeengine.com/cube.php4
Cube2 (Sauerbraten) - bigger and better cube http://sauerbraten.org/
DarkPlaces - One of the most advanced free software Quake engines http://icculus.org/twilight/darkplaces/
Delta3d - Integrates other well-known free software projects into an easy-to-use API, originally developed by the U.S. Navy http://www.delta3d.org/
DGD - An object-oriented programmable MUD engine http://www.dworkin.nl/dgd/
Doom engines - The now free software engine originally used for Doom and Doom II http://games.moria.org.uk/doom/du/engines.html
DXFramework - A simple, pedagogical 2D/3D DirectX-based game engine for Visual Studio http://dxframework.org/
DX Studio - Real-time professional 3D engine and editing suite produced by Worldweaver Ltd http://www.dxstudio.com/
*** Eclipse - A 2D MMORPG maker (Open source) http://www.freemmorpgmaker.com/
Elysium Source - A 2D online game engine made with VB6 http://splamm.com/elysium/
Epee Engine -Is an 2D/3D open source cross platform graphics engine with beginning programmers in mind http://www.epeeengine.org/
Eternity Engine - A source port of the Doom engine Exult - A free software reimplementation of the Ultima VII game engine http://www.doomworld.com/eternity/
FIFE - A free software 2D ISO engine supporting the assets of Fallout 1 & 2 http://www.fifengine.de/
Game Blender - A sub-application of Blender for creating games http://www.blender.org/development/rele ... e-blender/
Game Maker (current version 7)- Object-oriented game development software with drag-and-drop interface and its own scripting language http://www.yoyogames.com/make
GQ - A Quake engine that adds features from TomazQuake and DarkPlaces http://gzone.planetquake.gamespy.com/
GZDoom - A source port of the Doom engine based on ZDoom http://grafzahl.drdteam.org/
Genesis3D - A real-time 3D engine for Windows http://www.genesis3d.com/
GemRB - A free software implementation of the Infinity Engine http://gemrb.sourceforge.net/ OR http://en.wikipedia.org/wiki/GemRB
Irrlicht Engine - A cross-platform and lightweight three dimensional graphics engine. http://irrlicht.sourceforge.net/
Jogre - a Java based client/server game engine and API for online real time games such as chess, checkers, etc.
MRPGe - Visual Basic 2D RPG game engine, with built-in scripting capabilities. Very customizable, in early development stages.
M.U.G.E.N - A 2D fighting game engine
Multiverse Network - an MMOG platform, including server, client, and tools. (Free for development and use--revenue sharing upon commercial deployment). http://www.multiverse.net/
Nebula Device - A realtime 3D game engine developed by German game studio Radon Labs. http://nebuladevice.cubik.org/
NeoEngine / Evolution - GPL game engines http://www.neoengine.org/
OctLight - A Java game engine that uses scene-graph and renders on top of Lightweight Java Game Library (LWJGL) using OpenGL https://jge.dev.java.net/
Open Game Engine - is an open source library combining the components used to make games.
Currently used in PB 4+
OGRE Engine - A very popular object-oriented graphics rendering engine. Also called OGRE3D http://www.ogre3d.org/
Online RPG Maker - An Online RPG/2D engine with scripting.
Panda3D Engine - Rapid development engine based on Python http://www.panda3d.org/
Pentagram - A project to create a game engine that is capable of running Ultima VIII: Pagan http://pentagram.sourceforge.net/faq.php
PlayerWorlds - a simple, and widely used 2D Online RPG Engine. http://www.onrpg.com/contentid-3.html
PLIB - A game engine - includes 3D, Audio, Music, GUI, Window manager and is portable Linux/Windows/MacOSX.
ProQuake - A modified Quake engine http://proquake.planetquake.gamespy.com/
Quake II engine - The original free software Quake II engine from Id Software http://www.idsoftware.com/business/techdownloads/
Quake III engine - The original free software Quake III engine from Id Software
Reality Factory - A free open-source game engine that is intended for non-programmers and is built on the Genesis3d Graphic Engine. http://www.realityfactory.info/cms/
RealmForge - An open-source game engine for the Microsoft .NET Framework, predecessor to Visual3D.NET http://sourceforge.net/projects/realmforge
RPG MAKER XP - About what it says it is http://www.enterbrain.co.jp/tkool/RPG_X ... tions.html
Stratagus - A cross-platform real time strategy game engine http://www.stratagus.org/
Telejano - a modified Quake engine http://telejano.berlios.de/
Tenebrae - One of many Quake engine clones http://tenebrae.sourceforge.net/
Toi - A 3d game engine currently in development with promises of both MMO and single player capabilities. Free but with licensing fees that are to be announced. Has much potential.
vbGORE - Open-source online RPG engine in Visual Basic 6 (2d via 3d hybrid engine).
Well of Souls - A 2D engine with scripting in QUEST and a visual world editor. http://www.synthetic-reality.com/
Yake - a component-based, object-oriented, partially generic engine written in C++ http://www.yake.org/
Zak Engine - An easy to use 2D games engine using DirectX 8.1 and 9 developed for novice and professional programmers. Features: sprites, tiles maps, sound and music in several formats, scripting (AngelScript), particle systems and more! http://www.zakengine.com/ (Español) - http://translate.google.com/translate?h ... f%26sa%3DG - ENGLISH (I THINK)
There must be more.
That was a lot of editing!
