Caustic

Probably the best portable music app available for Android. It has the ability to do just about everything, can export audio and midi, it's easy to learn and fantastic value for money. I use causeic as a scratchpad for when I have ideas away from my studio space, but I've also used it as part of live performance and as an instrument into my home studio. Highly recommended. It's very similar to early versions of reason, but for a reasonable price (badum tish). Hasn't been updated in a while but it's very stable and complete so it doesn't "need" updating as such, but a granular synth or some new effects might be a nice addition to the already massive feature set. Get this app. Just get it.