3Impact: Impact, modelling and car library for games. Includes screenshots and downloads of demos. [Commercial]
Betatron: For the creation of 2D-platform and action-arcade games in C++ for the DJGPP v2.0 compiler. [Open Source]
ClanLib: A multi-platform game development library. Currently is works on Linux and Win32. [Open source, LGPL]
Clean Game Library: A complete development system for 2D games (arcade, side scrollers, platform games), using the functional language Clean.
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.
DRP Automotive Dynamics: Vehicles dynamics and damage modelling SDKs. Vehicle sample packs.
GapiDraw: A complete toolkit to create games for handheld devices. [Free for non-comercial use]
Golden T Game Engine: A Java library for creating 2D games. [Freeware]
HGE: Haaf's Game Engine: A C/C++ library for creating hardware accelerated 2D games for Microsoft Windows. It provides minimal yet fully functional and flexible set of routines for handling graphics, sound and input. [Shareware]
IsoEngine: A Visual Basic/C++/.NET isometric/2d game engine. [Commercial]
Jet3D: A (commercial) free and open source realtime 3D graphics engine and SDK.
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.
Object oriented Simple Directmedia Layer: OSDL, a free portable high-level open-source library for multimedia and game programming.
PathLib: Pathfinding library for games, optimal paths through maps, timing objects and their movements through maps. Sample application available.
RAD Gametools: Develops game software technologies which are licensed by primarily by video game companies.
RakNet: A game orientated networking API that is a wrapper for Berkely Sockets on Windows, Linux, and Unix. [Commercial]
Regimental Command: A generic armored combat system.
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.
The Yake Engine: A small, flexible, cross-platform game engine / application framework multi licensed under the LGPL and custom licenses.
Titan: A C++ based library to load/save game-related file formats, such as graphics, sound and 3d meshes.
VgaGames: A free library for programming vga games (320x200 pixels with 256 colors) for Linux and FreeBSD in C. [Open source, GPL]