OFFICIAL PAGE: Stem Isolator
Stem Isolator, by Origin Audio, is a web-based service for separating your audio into stems. It allows you to upload a source file which will be separated into 2 stems (Vocals and other), 4 stems (Vocals, drums, bass and other), or 5 stems (Vocals, drums, bass, piano and other). The service accepts wav, wavex, flac, aif and aiff files. The service is offered with various pricing plans and offers a number of tools in each plan in addition to the Stem Isolator. Full details at the link above.
Screenshot courtesy of Origin Audio