Only available on Iphone, is now for the first time, it's for Android and the app is better than when it's on Iphone.
"First thing I need to mention is that Instagram is a lot more than just a free photo enhancement app for your phone. It connects its users to a photo-based social network that's over 30 million users strong. With this powerful social functionality, the app makes it incredibly easy to not just polish and share photos, but also to keep tabs on friends through the built-in Instagram photo stream. So it looks like the answer is yes, Instagram's got a bit of Tumblr blood in it, and that's good."
Go here for more info:
You can download from the Market (Google Play).