Figure is so much fun
Propellerhead's Figure is ancient, having launched in 2012 - you could download it for your iPod Touch. It's still a great time, though, a kind of fool-proof musical sketchpad. Where other apps confront you with endless options, Figure offers you three tracks: drums, bass, and lead. You build patterns by selecting rhythm and scale parameters, but you don't actually have to know anything about how drum patterns or scales work, as Figure does all the quantizing and transposing and whatnot. You can literally just stab your fingers at the screen and produce interesting bits of music. A more considered approach can yield surprisingly sophisticated results. For instance, you can manipulate various parameters for each instrument, and bake them into your tune with automation. You can produce and save endless variations of patterns to import into a sampler or DAW as the basis for a song; you can also save each instrument as a stem by muting the other two and creating a separate save.
The variety and quality of onboard sounds is impressive, but it's strange that they never introduced optional expansion packs, or allowed users to upload their own samples. The app's most glaring shortfall is its lack of MIDI export. Still, in terms of sheer accessibility and fun at a stupidly low price, Figure remains hard to beat.