OFFICIAL PAGE: DEMIXOR
DEMIXOR is a web-based service for separating an audio source file into stems. It allows you to upload a source file, which will be separated for a fee into up to 4 stems (Bass, Drums, Vocal, Other). The service claims to be using artificial intelligence (AI) to perform the separation. For more details visit the website at the above link.
Screenshot courtesy of DEMIXOR.com