Grit Game Engine - The Grit Game Engine is an MIT-Licensed Open Source Game Engine that is highly scriptable via Lua.
Pygame - Pygame is a set of Python modules designed for writing games.
Unity - The multiplatform game creation tools for everyone.
Torque 3D - Torque 3D is a easy-to-use game creation platform.
Unigine - Unigine Engine is a proprietary cross-platform middleware, developed by Unigine Corp.
irrlicht - This caused the Irrlicht homepage and forum to work badly. Over the last days most things started working again – except the forum continues to be broken. Old posts can be read but everything else is currently not working.