There’s a new sampler box soon to be announced by Torso, the S-4, and someone asked on the pre-release thread if there was an iPad app that did something similar.
I half-facetiously replied “Drambo”, but I don’t really know. My experience with working with samples is pretty much limited to Digitakt and PO-33. I’ve never touched an Octatrack or SP-404. On my iPad, I own Koala and Drambo (bought on sale) but I’ve only poked at them briefly. Loopy Pro is on my to-buy list. I’d be curious whether those with more experience could comment on how these or any other iOS apps could do most of what the S-4 seems to do (we only have incomplete information from a leak so far, no official announcement).