Agar
A graphical game engine aimed primarily at applications ranging from SDL 2D games to multithreaded 3D simulations. The engine currently implements tile-based levels, a level editor, a GUI, and various other interfaces for game programming. [Open source, BSD License]

Betatron
For the creation of 2D-platform and action-arcade games in C++ for the DJGPP v2.0 compiler. [Open Source]

Blade's PSX Programming Libraries
A free C compiler and libraries for Sony PlayStation game programming. You Would also find info related to psx dev psxdev caetla tools yarouze yaroze compiler ezoray homebrew console programmingmips r3000 assembler playstation development kit libps.exe psyq psy-q blade libraries and much more.

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. You Would also find info related to Clean functional programming games side scrolling platform games DirectX and much more.

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] You Would also find info related to gapi, gapidraw, pocket pc, smartphone, directdraw, directx, game, sdk, software development kit and much more.

Hyperion Project
Set of components which handle the deformation of solids in real time. Special FEM adaptation. You Would also find info related to Ephydryne, FEM, Finite Element Method, video game, deformation, real-time, physical simulation and much more.

ika
A Windows based game engine designed to allow one to make a console style RPG with a minimum of code, while allowing one who is willing to code an impressive level of power over the look and feel of one's project, thanks to the embedded Python interpreter. [Open source, GPL]

IsoEngine
A Visual Basic/C++/.NET isometric/2d game engine. [Commercial] You Would also find info related to isoengine, isoengine sdk, isometric, engine, programming, visual basic, game, vb, iso, sdk, map editor, isometric engine, isometric game engine, isometric game, iso engine, game programming, isometric programming and much more.

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.

MoleStudio SpriteCraft
An easy-to-use 2D game engine. It can be used in any programming language suppoting COM.

Object oriented Simple Directmedia Layer (OSDL)
A project, aiming at providing a portable open source high level library to ease multimedia and game programming. You Would also find info related to video game, libray, open-source and much more.

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] You Would also find info related to free network library dplay voice directplay windows direct play udp ip ipx client server peer game and much more.

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.