The wonderful fretless Geo. One of my favourite apps of all time. Can produce amazing sounds as a synth and as a midi controller. If you play guitar or bass and like synths, this is a great interface. On a side note, Geo was created by Rob Fielding and passed around to a few different developers since, leading me to this.. Geo is the high school hooker of the music app world, she has been in bed with at least 4-5 guys since i known her!