Roland's Sound Canvas modules were ubiquitous throughout the '90s, offering stock sounds that were often used by computer users with MIDI sequencers (software instruments were still glints in developers' eyes back then, remember).
Now – and like pretty much everything else, it seems - the Sound Canvas is returning as an iOS app. This GM-, GM2- and GS-compatible module also features a MIDI file player and effects, and offers a total of 1,600 tones and 63 drum sets.
It could be worth a look if you're feeling nostalgic, though it appears that, as things stand, there's no Audiobus support. Reviewers on the App Store are also noting that there are problems with the Inter-App Audio implementation, so its usefulness in your wider iOS music making setup could be limited at the moment.