This is a breakout board for the STM32F401RCT6 microcontroller. It has a built-in ST-Link programmer just like ST's discovery boards. It also has a reset button, 8-MHz HSE crystal, and jumper pins for the BOOT0 and the virtual COM port.
- STM32F401 Reference Manual
- Custom ST-Link V2.0 / V2.1 / V3.0
- Reference for the hardware and the firmware of ST-Link programmer.