Piotr Esden-Tempski of 1Bitsquared created this Open Source and Open Hardware debuggable ARM development platform:

1Bitsy

Firmware development with the lights on

Design files and source code are shared on GitHub:

1bitsy-hardware

Small breadboard friendly STM32 (eventually other mcu’s too) eval boards with exposed JTAG and SWD for the use with Black Magic Probe and others!

1bitsy-examples

Example projects for the 1BitSy development board