Renoise
From Just Solve the File Format Problem
Renoise is a commercial digital audio workstation for Windows, macOS, and Linux with a workflow and interface inspired by music trackers. The demo version of Renoise can save, load, and play, but cannot export audio files.
Renoise's three major binary file formats are the song file (XRNS), instrument file (XRNI), and effect chain file (XRNT). XRNT files are just plaintext XML files, and XRNS and XRNI files are ZIP archives containing an XML file and some audio files in familiar formats (WAV, FLAC, MP3, etc.). The XML files are readable, almost self-documenting, and schemas can be found for free in the demo distribution.