PrBoom is a game engine for playing Doom levels, which runs on both Windows and POSIX systems. It uses the SDL graphics library.
Pyzzle is a free and open source cross platform Myst/Riven interface style game engine.
Q-Gears is an attempt to make a clone of Squaresoft's Final Fantasy 7 game engine. It is designed to be cross-platform and run on modern operating systems such as Win32 and Linux.
qtour is a Qt-based GUI application for interpretation of sporting tournaments. It uses the libtour C++ library as its processing engine. qtour is released under the GNU General Public License.
Quad-Ren is a resolution independent 2D graphics engine that aims to ease the development of bitmap-based applications, primarily games. It will run regardless of screen resolution or aspect ratio, and works flawlessly with tiling window managers. It rectifies many of the issues with older methods of 2D game development such as color key transparency (which inevitably leads to aliasing) and having to draw sprites in a specific order, which Quad-Ren handles using alpha transparency and layers respectfully. It is programmed in, and usable from C++, with a simple object-oriented API and a small, well documented, easy to edit code base.
QuakeForge is a 3D graphics game engine based on id Software's legendary Quake and QuakeWorld game engine. Our purpose? To improve the state of the game by improving the engine and making it accessable to the largest number of players we can.
Raydium is a small 3D engine which uses OpenGL which attempts to be easy-to-use and portable. It has been tested on Linux and Windows, but it should work on any system with GL, GLU, and GLUT.
RealmForge GDK is a cross-platform game development framework and toolkit written in Mono/C# and powered by the Axiom 3D engine. It will allow for the rapid development of cutting-edge script & data-driven games and MMORPGs.
REminiscence is a rewrite of the engine used in the game Flashback from Delphine Software. This program is designed as a cross-platform replacement for the original executable and uses the SDL library.
Sauerbraten game engine
Sauerbraten is a 3D game engine (more powerful redesign of the Cube engine) and FPS/RPG game
Scrupp is a 2D engine that uses OpenGL for hardware-accelerated visualization. All of its functionality is exported to the Lua programming language.
sge2d, also known as SDL Game Engine, is a platform-independent 2D game programming framework for C programmers with the least possible dependencies for easy porting and with a focus on easy API calls and the requirement of commercial programmers
Shadowplay is a game framework that makes it easy to write games that use video as the input. It is inspired by the Indie Game Jam 01 and the EyeToy.
Siriel4 is a game engine for adventure, arcade or maze games featuring scripting, music and audio support.
Soya 3D is a very high level 3D engine for Python. Soya aims at being to 3D what Python is to programming : fast to learn, easy to use, while keeping good performance! Our goal is to propose a complete architecture to realise free (GPL) games with professional quality entirely in Python.
Spearmint is an extended Quake III Arena engine for creating standalone games. Includes various features from RTCW, WolfET, Tremulous, and World of Padman.
Spectalum is a reverse engineered Open Source game engine for the 1991 CRPG Eye of the Beholder II: The Legend of Darkmoon originally developed by Westwood Associates.
Sphere RPG Engine
Sphere RPG Engine is a console-style RPG engine that allows others to create an RPG similar to Final Fantasy, Dragon Quest, or Phantasy Star.
Spineless Jelly is a generic cross-platform 3D game engine implemented in Python with Pyrex optimizations. Focus is on flexibility, clean design and ease of use, not pure speed or bleeding edge graphics.
Stratagus is a free cross-platform real-time strategy gaming engine. It includes support for playing over the internet/LAN, or playing a computer opponent. The engine is configurable and can be used to create games with a wide-range of features specific to your needs.
The Gamebook Engine
The Gamebook Engine is a cross-platform engine for writing gamebooks, such as the "Choose Your Own Adventure" series or the "Lone Wolf" series. TGE can interpret scripts that use the "Hyena" gamebook format.
Wurld is yet another free 3D gaming engine. It is light, fast, has minimal external requirements, and is still very immature. It is Python scriptable, including support for generating models using 3D turtle graphics.
TuxCap Games Framework
The TuxCap games framework is a GNU/Linux port of PopCap's games framework, which is a commonly used framework for professional casual game development on Windows.
xoreos will be a reimplementation of BioWare's Aurora engine (and derivatives).