Frictional Games has released the source code (http://github.com/FrictionalGames) for their first game Penumbra: Overture, together with the source code for the engine and tools used in its creation.

This comes as a reply to the great success of the Humble Indie Bundle, in which over US$1 million dollars has been donated to the participating developers and charities, says Thomas Grip, programmer and co-founder of Frictional Games. Apart from Penumbra, the source codes for the indie games Aquaria, Gish and Lugaru (all available in the Humble Indie Bundle) are also released.

Penumbra: Overture contains a unique physics interaction system for first person games, a system that has been exclusive to the series and not found in any other game, Grip says. The source code is currently running on Windows, Mac OS X and Linux.

The source code has been uploaded to GitHub where it is easy for people to download the latest version, suggest patches, make new versions of the code and much more. To kick start the development Frictional Games has also put up a dedicated section in their forum, where people can discuss the code and more.