As promised when the Humble Indie Bundle hit $1 million in donations the other day, indie developer Frictional Games has released Penumbra: Overture's source code. "The code for Penumbra: Overture is a continuation of the one used for the tech demo + some addition for the not so long lived Robo Hatch project. It also contains some code from Unbirth, giving it quite some history." The release also includes the HPL1 engine. "This is engine that has powered all of the Penumbra games and it even includes the stuff used to create the 2D platformer Energetic. The engine code was started in December 2004 and was actively developed until early 2008." The repositories are available at github.