Dirtywave M8 Tracker

The Dirtywave M8 is a Teensy-based device that provides a tracker-like interface for music creation in a portable device.

Its firmware is freely available and can be run on a standalone Teensy 4.1 (which negates a lot of the advantages of having standalone hardware, but makes for a very nice teaser to assess if it is the right tool for you), and that has inspired a number of breakaway projects: