PDDuino
Jimmy Petit's original project for Arduino Mega
And here is a fork that adds,
- power saving sleep mode calls
- disk-activity led
- support for the special card-reader hardware on Teensy 3.5/3.6
- support Adafruit Feather 32u4 Adalogger (now also the Feather M0 Adalogger)
- the current working directory is displayed in the top-right corner of the TS-DOS display