Just thought I would share, Frictional made two games they had done anything with Penumbra.
The first game is Fiend. It was released in 2001.
Here is a link to frictionals page of it,
http://www.frictionalgames.com/site/fiend the page can't be found anywhere in on frictionald site other then the URL.
There second game was Energetic, made in the HPL engine, probably before the engine was even named. They released it in 2005 (I think) So here is the link for this one!
http://www.frictionalgames.com/site/energetic/
These are both rather interesting games, they are both free and the download button is on the side.
Have fun! Glad I could share these for people who don't know about them!
(Energetic was actually the first of their games that I played xD)