PC and Mac versions, now through Friday
There's something about the first-person shooters of the '90s that makes them (some of them) still hold up to this day. I mean, Duke Nukem 3D shouldn't be aesthetically pleasing to me in 2012, but the old sprite-based characters are oddly charming, and these titles tended to move at a pace we don't always get with modern shooters. Plus, they were ridiculous.
Considering that Duke Nukem 3D: Atomic Edition is currently free for PC and Mac on GOG.com, much of that justification was probably unnecessary, but there you go. If you are looking for a way to relive a bit of Duke history, you can't go wrong with this deal.