Free Game Programming Libraries

Torque 3D
Torque 3D is an open source 3D game engine. Torque 3D comes equipped with a full suite of tools and produces high-quality games and simulations. Supports Windows and Browser-based web deployment out of the box.

This is an open-source 3D game engine written in Java and designed for Java programmers who want to develop games. There are some examples games, including at least one open-source first person shooter game available by clicking the Showcase link.

Libraries of wrappers written in C# (free source) for for 3d graphics audio or compute functionality (OpenGL, OpenCL and OpenAL.). There is also an open-source wrapper for the DirectX API under the .NET platform, and a networking library for the .NET Framework with a client/server API. It's goal is to allow XNA developers on Xbox 360, Windows & Windows Phone to port their games to the iOS, Android, Mac OS X, Linux and Windows 8 Metro.

The G3D Innovation Engine is a commercial-grade C++ 3D engine available as Open Source (BSD License).

Panda3D is a 3D engine: a library of subroutines for 3D rendering and game development. The library is C++ with a set of Python bindings. Game development with Panda3D usually consists of writing a Python program that controls the the Panda3D library.

Irrlicht Engine
The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++ and also available for .NET languages. It is completely cross-platform, using D3D, OpenGL and its own software renderer, and has all of the state-of-the-art features which can be found in commercial 3d engines.

Blender3D is open source software for 3D modeling, animation, rendering, post-production, interactive creation and playback.

Simple DirectMedia Layer
Simple DirectMedia Layer is a cross-platform multimedia library designed to provide low level access to audio, keyboard, mouse, joystick, 3D hardware via OpenGL, and 2D video framebuffer. It is used by MPEG playback software, emulators, and many popular games. SDL officially supports Windows, Mac OS X, Linux, iOS, and Android.

Jet3D is a robust 3D graphics engine built for high performance real-time rendering. Jet3D offers realtime editing, advanced lighting features, 3D modeling support, seamless soft-skin polygonal characters and many other innovations. Check the website for licensing details.

QuakeForge is a 3D graphics game engine based on id Software's legendary Quake and QuakeWorld game engines.

Golden T Game Engine
Golden T Game Engine (GTGE) is a Java library for creating 2D games.

Crystal Space
Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. Cross-platform (Windows, GNU/Linux, Mac OS X).

Pygame is a set of Python modules designed for writing games. It is written on top of the excellent SDL library. This allows you to create fully featured games and multimedia programs in the python language. Pygame is highly portable and runs on nearly every platform and operating system

Retribution Engine
The Retribution Engine is designed for first person action games on Windows PCs using OpenGL and OpenAL. It is supplied with a wide range of games and levels and includes fully featured level and model editor.

Adventure Game Studio
Free 2d point and click adventure game creation suite with smart and flexible scripting language.

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.

Genesis3D is an Open Source 3D Game Development Engine, with a license designed to allow use of the game in commercial, or non-commercial applications for free. See the site faq for licensing details and requirements.

PLIB: A Suite of Portable Game Libraries.
PLIB includes sound effects, music, a complete 3D engine, font rendering, a GUI, networking, 3D math library and a collection of handy utility functions. All are 100% portable across nearly all modern computing platforms.

2D graphics library with support for multiple output devices. Currently supported output targets include the X Window System (via both Xlib and XCB), Quartz, Win32, image buffers, PostScript, PDF, and SVG file output. Experimental backends include OpenGL, BeOS, OS/2, and DirectFB

Wintermute Engine
Freeware, state-of-art adventure game engine that makes it possible for independent developers to create adventure games of commercial quality. Flexible scripting language gives the developer significant degree of creative freedom. Community-developed plugins provide additional functionality.

Doom source code
This is a link to an ftp download of a zip containing the Doom source code.

Allegro is a game programming library for C/C++ developers distributed freely, supporting the following platforms: DOS, Unix (Linux, FreeBSD, Irix, Solaris), Windows, QNX, and BeOS (MacOS port is in alpha stage).

OGRE 3D engine
OGRE (Object-Oriented Graphics Rendering Engine) is a scene-oriented, flexible 3D engine written in C++. The class library abstracts all the details of using the underlying system libraries like Direct3D and OpenGL.

PPTactical Engine
PPTactical is an engine for real-time strategy and real-time tactics games, developed in opensource fashion.

JOGRE (Java Online Gaming Real-time Engine) is an open-source, online, real-time games engine and API programmed entirely in Java.

Wolfenstein Source Code
This is an ftp download link to the free 3D engine for Wolfenstein.

Crystal Space
Crystal Space is a free (LGPL) and portable 3D Game Development Kit written in C++. Cross-platform (Windows, GNU/Linux, Mac OS X).

SCI Studio
SCI Studio is a completely free game development system for Sierra's SCI game engine. It allows you to create games like Sierra's King's Quest, Space Quest, Police Quest, Leisure Suit Larry etc.

An open source 3D virtual world for Linux and OpenGL, OBSIDIAN is an extensible virtual world system with a fullblown multiplayer client-server architecture.