Codeweavers makes really cool software called CrossOver that lets Mac and Linux users run Windows software on their computers. There are two versions: CrossOver Pro, which installs and runs lots of office-y stuff, and CrossOver Games, which does exactly what it sounds like. Quoth Wikipedia:
CrossOver (known before version 6.0 as CrossOver Office) is the collective name for three commercial and proprietary programs developed by CodeWeavers that allows many Windows-based applications to run on Linux, Mac OS X and Solaris using a compatibility layer. The programs include CrossOver Mac, CrossOver Linux and CrossOver Games.
The programs are tweaked, proprietary versions of the public Wine source tree with various compatibility patches added, more user-friendly configuration tools and commercial support. CodeWeavers employs several Wine developers and contributes code back to the free software/open source software Wine project as per the GNU LGPL, although CrossOver itself is proprietary software.
I'm a big fan of CrossOver. Before Pokerstars released their Mac client, I used CrossOver to play in tourneys for years on both my Linux machine and my Mac. If you're a Mac or Linux user and you want or need to run Windows software on your machine, including a bunch of spiffy games, head over to Codeweavers and get to downloading.
ETA: The Unofficial Apple Weblog explains why Codeweavers is doing this today. Pretty awesome.