For those of you that don't know, Hidden Path (the folks behind Defense Grid) launched a kickstarter project last summer to raise funding for a sequel to the original game, and/or additional content for the first game.
DG2 is scheduled to be released in the first half of 2014, and will feature online multiplayer, Win/Mac/Linux support, and user generated content, on top of new entities, stories, and engine enhancements!
Even better, if you were a Kickstarter backer, you get a copy of DG2 for free!