LOVE, a project seeking to redefine pretty much any core assumptions about the genre. Players build and create, levels are based upon relationships with other players, and the entire world is a surrealistic masterpiece of a landscape. Oh, and the entire project is the work of one man, Eskil Steenberg. It's the sort of thing that would be well worth checking out, and during the holiday weekend, you can do precisely that.
From 6 PM GMT on Friday until noon on Monday, LOVE will be having its first free weekend, giving players curious about the actual mechanics of the game a chance to log in and take a close look at how the game works. That runs the majority of the Labor Day weekend, a fine time to log in and get some serious construction going. Keep an eye on the official site or on GamingLove for more information on registration.
[Thanks to bartillo for the tip!]