Pantha Rei is a collaborative game engine and toolset.
It is a collaborative gaming environment, aimed on estabilishing a community of players, developers, a toolset, and actual games. Fully GPL-ed with support for non-free and/or paid modules and content. Developed in python. Leverages various successful components such as Python-OGRE, Python-GTK, pyGame, etc.
The ultimate goal is a distributed multiplayer adventure game, but smaller games - probably remakes of classics - are targeted first.
Product's homepage