QBlock is a cross-platform rapid-prototyping game design engine written in C++, SDL and OpenGL. Features game asset management, scrolling tilemaps, particle systems, 3D model support, Lua scripting and more.
Roc's purpose is to serve as a tool for those who know little about programming. It strives to create RPGs similar to those on your video game console. Roc is written in Python and wxPython. It will support all platforms compatible with wxPython.
Mallard is a graphical game design package, akin to many applications for Windows such as The Games Factory, RPG Maker, Game Maker, etc. It is written in Python with wxWidgets and PyGame, and therefore should support any OS which supports Python and SDL.
PsychoEngine is an Open-Source WYSIWYG 3Dgame engine/creation utility, that hopes to eventually compete with other Open-Source game engines/creation tools as well as commercial engines and tools, both visually and in playablity.