I like, and use, FL mobile. Good for messing about on the train (those were the days) before sticking patterns into fl studio.
Kaossilator was free for a while and enjoyable.
FakeSID was surprisingly nice also.
Chordbot is super handy for generating midi progressions to send to a daw.
Sunvox developer has also made PIXITRACKER which has 8bit and 1bit versions. Superintuitive and sound great.