Today, Indie-ana Co-Op goes on an adventure in the wide world of iPhone/iPad gaming. The common theme for this installment? Zombies. Two different takes on the theme are investigated: Tweet Defense and Alive 4-Ever Returns.

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!

Last month we told you about Tweet Defense, a unique take on the desktop tower defense genre.  Games like Pixel Junk Monsters and Comet Crash have added co-op to the genre, allowing direct player interaction, but Tweet Defense is trying co-op a different why.

It's always interesting to see some unique form of cooperative play pop up, such as that which is coming in TweetDefense.  The iPhone and iPod Touch game mashes up zombie survival modes with the tower defense genre and throws in Twitter for good measure.  Twitter?  Yes THAT Twitter.