Rich Music Format
From Just Solve the File Format Problem
Rich Music Format is a proprietary audio file format designed by Beatnik, Inc. for their open-source miniBAE sound engine to allow simultaneous playback of MIDI and digitized audio.
-  The miniBAE source code. Includes documentation on the RMF format.
- . Latest Wayback Machine capture of beatnik.com, in case anyone wants to try and grab those PDFs.
- RMF - Rich Music Format on music-notation.info.