Starcraft II test server that they want fans to try out and put through their paces before they're made official mods.
The inventive mods include:
Aiur Chef is a cooking game in which you explore the map, and find ingredients to complete a dish before your opponents can. StarJeweled, a puzzle-strategy mod, involves playing Bejeweled-like grids to make energy to build units with which to attack your opponent.
Left 2 Die is a fun take on Left 4 Dead, in which a player and a friend fend off a neverending stream of Zerg rushes. They only come out at night, though, so you and your friend can build and recruit during the daytime to prepare for the onslaught. There's even a version called Night 2 Die, in which you suffer through an eternal night, so there's no break as wave upon wave of infested attack.
To test these out, go to the Multiplayer tab in StarCraft II and look in the custom games window.