Paranautical Activity is back on Steam under the moniker Paranautical Activity: Deluxe Atonement Edition. So what is this atoning for, exactly?
Paranautical Activity was removed from Steam when its creator threatened to kill Gabe Newell. Gaming enthusiasts may disagree about a lot of things, but I think we can all come together under a shared understanding that that was a silly thing to do.
Anyway, sometime after that, er, 'incident', developer Code Avarice sold the rights to Paranautical Activity to someone else. That someone was Digerati Distribution, and, as a result, the game has been allowed back onto Steam.
As part of the updated edition, the FPS roguelike now includes an extra level type, weapon and item. Here is a trailer:
Paranautical Activity is also available on GOG.