Open-source, cross-platform, game-development tools
Extensible HTML5 app for real-time collaborative projects
486 lines of C++: old-school FPS in a weekend
A minimalist and cross platform System Shock source port
Build Cross-platform Applications
MMORPG
C/C++ , PHP, PYTHON, 3D ENGINES, CHROME NATIVE CLIENT
scriptable game engine with built-in support for 2D graphics and sound
3D .NET engine for Windows, Linux, Mac
A game engine written in the D programming language
A Flash Molehill (Stage3D) GPU accelerated 2D game engine
a very lightweight advanced terrain-rendering and 3D map rendering sys
Plugin based multi-purpose dev tool.
Pygrid is an open-source and cross-platform pygame/python 2D engine.
The Flixel Power Tools are a set of plug-ins for Flixel 2.5+
A graphics engine + toolkit.
Graph editing tool
Cross platform 2D game creation framework with Python bindings