I've been looking into this stuff extensively, but I'm still not sure... which app is closest to garageband? What I'm looking for is the ability to create "professional" songs, without anything but the one app. I'm looking for multiple instruments, multiple tracks at once, an actual note editor for each track, saving, loading, creating, the works on a smaller level.
As far as I know Beatmaker is probably the closest to that. I'm not sure exactly what you mean by "note editor" but you can change the tone of each sample. So if you had a single flute sample you could turn it into eight different samples that would make a scale. You can only have 16 samples available at once to choose from for each project though (there is a slightly tedious workaround to this that involves using your computer). You can have an endless number of patterns/tracks going in your project. You can save, load, create, export as .wav or .midi, load your own custom samples and kits. There are two FX channels and a clean channel. The available effects are Delay, EQ, Bitcrusher and a filter that can be set for high pass, lowpass or band filter. You can assign any sample to either FX track or the clean main track. Tracks can be as long and complex as you want them to be. There is onboard pitch editing, panning and waveform edit. There are other features but those are the highlights I guess.