Theres a F2P called Mabinogi. Played it a bit, and you could compose songs for instruments kinda like a Midi file. Was pretty fun, but the interface for composing was...horid, so folks made some tools to make it easier.

Was pretty fun trying to make new tunes. Not sure if its doable, or even a good idea for FF14, but it was definately something that kept me busy and having fun for a while.