We've covered Tweet Defense a couple times here at Co-Optimus. It's an odd blend of Tower Defense, zombies, and social networking via Twitter. These are three things I generally enjoy very much, but I never took the plunge and checked it out. Today, there's no excuse, as Tweet Defense is available at no charge for one day only. The game is available for the iPhone/iPod here, and for iPad users right here. Since your effectiveness in game is boosted by your Twitter stats, why not go ahead and follow Co-Optimus on Twitter, if you haven't already, and check out the staff page and follow us there as well!