Circadia is a great game that I wrote about a little over a year ago -- it's put together by a developer named Kurt Bieg, and until now, it's basically just been sitting on the App Store waiting to be found. But Bieg has just put out a nice solid update for the game, and that gives me another chance to recommend it to you.
The game is simple and ingenious -- it's musical, but the music of it is what you make yourself rather than the pop songs that you'll find in Rock Band or other music titles. Beig says in the latest App Store update that the game has reached 100,000 downloads, and that's a great number for a little title like this. He's updated the title to make it work with the iPhone 5, and there's also a new "infinity mode," featuring randomly generated levels that you can play anytime you like. There are also new tone sounds, which is a pretty impressive feat on Bieg's part, and finally there's an in-app purchase to just unlock all the levels, if you happened to be stuck on a certain one.
This update really makes this app shine, and if you didn't see it last year, you should definitely take a look now. Circadia is available as a universal app right now for US$0.99.