ClanLib A multi-platform game development library. Currently is works on Linux and Win32. [Open source, LGPL] http://www.clanlib.org/

Jet3D A (commercial) free and open source realtime 3D graphics engine and SDK. http://jetpp.sourceforge.net/

Blade's PSX Programming Libraries A free C compiler and libraries for Sony PlayStation game programming. http://www.blade.ip3.com/

MIDAS Digital Audio System MIDAS is a multichannel digital sound system. It supports DOS, Win32, and Linux platforms and plays Protracker (.mod), Scream Tracker 3 (.s3m), FastTracker 2 (.xm) and Impulse Tracker (.it) modules, as well as samples and audio streams in raw or WAVE . MIDAS is free for non-commercial usage. http://www.s2.org/midas/

RakNet A game orientated networking API that is a wrapper for Berkely Sockets on Windows, Linux, and Unix. [Commercial] http://www.rakkarsoft.com/

GapiDraw A complete toolkit to create games for handheld devices. [Free for non-comercial use] http://www.gapidraw.com/

RAD Gametools Develops game software technologies which are licensed by primarily by video game companies. http://www.smacker.com/

PathLib Pathfinding library for games, optimal paths through maps, timing objects and their movements through maps. Sample application available. http://pathlib.hildebrand.cz/pathlib.html

Titan A C++ based library to load/save game-related file formats, such as graphics, sound and 3d meshes. http://titan.sourceforge.net/

The Photon Effect libCON DirectX C++ libraries and ColDet collision detection libraries. Documentation, tools, code examples, and game skeletons available. http://photoneffect.com/default.html

Betatron For the creation of 2D-platform and action-arcade games in C++ for the DJGPP v2.0 compiler. [Open Source] http://www.geocities.com/SiliconValley/Horizon/8630/

Hyperion Project Set of components which handle the deformation of solids in real time. Special FEM adaptation. http://membres.lycos.fr/lagrandeporte/hyperion/

Regimental Command A generic armored combat system. http://regcom.sourceforge.net/

VgaGames A free library for programming vga games (320x200 pixels with 256 colors) for Linux and FreeBSD in C. [Open source, GPL] http://www.vgagames.de/index_en.html

The Grand Unified Toolkit (GUT) A cross-platform C++ API for the development of games and other forms of interactive media. It is available for the BeOS, Linux/X, and Win32 platforms. http://gut.sourceforge.net/

Clean Game Library A complete development system for 2D games (arcade, side scrollers, platform games), using the functional language Clean. http://cleangl.sourceforge.net/

DimensioneX Multiplayer Adventure Development Kit Offers a freeware Java software capable of building and running multiplayer adventure games, playable with any browser. Several multiplayer games are available for free as a demo. http://www.dimensionex.net/en/

MoleStudio SpriteCraft An easy-to-use 2D game engine. It can be used in any programming language suppoting COM. http://www.molestudio.com/tools/spritecraft/

IsoEngine A Visual Basic/C++/.NET isometric/2d game engine. [Commercial] http://www.firstproductions.com/soft/isoengine/

DRP Automotive Dynamics Vehicles dynamics and damage modelling SDKs. Vehicle sample packs. http://www.drpdynamics.com/