RetroArch is a frontend for emulators, game engines and media players.
RenderDoc is a stand-alone graphics debugging tool
A dead simple 2D game library for Go
Game engine supporting many 3D/2D formats and graphic effects
A promising chess program
Cerberus Content Management System
Web IDE in single HTML file
Free 32/64/16-bit multi-platform Pascal and Object Pascal compiler
A cross-platform interpreter for many point-and-click adventure games
Android, DOS, FirefoxOS, Linux, MacOS and Windows all in one..
Paintown is a 2d fighting game engine.
Cross platform Game Creation Software
The solution to all your problems
Very Powerfull Crossplatform Qt Based Music Note Editor[Still Planing]
DRINKS is a set of smart web-based widgets.