OFFICIAL PAGE: Let's Unmix (Apple App Store)
Let's Unmix, which makes use of Deep Learning technologies, is available as a free download for both the iPad and iPhone. The app will take a mono or stereo source file and return four stems: vocals, drums, bass, and the remaining music. The developer is charging US$4.99 as an in-app purchase to unlock the ability to save your results as compressed (AAC) or uncompressed (WAV) files. The app is available on the Apple App Store. Details are available at the link above.
Screenshot courtesy of Christopher Kissel