RetroArch is a frontend for emulators, game engines and media players.
Paintown is a 2d fighting game engine.
A cross-platform interpreter for many point-and-click adventure games
Portable Pokémon Mini Emulator
Android, DOS, FirefoxOS, Linux, MacOS and Windows all in one..
Cross Platform GUI Toolkit
Life Screensaver
Set of tools for the Sony PSP (tm).
Multi-platform game engine similar to old Megaman with a stage editor