The board used in this community contribution is a STM32F411CEU6 based board from WeAct Studio called MiniF4 F411CE, also known as Black Pill F411CE.
The pins can be used for several purposes, GPIO, PWM, I2C, SPI, SERIAL, etc.
Further details how the pin out is supposed to work can be found in the resources folder, of course since we know now what MCU pins go to what PCB pins we can change the board.h depending on what you want to achieve with the board.
For more information you may want to have a look at https://github.com/WeActTC/MiniSTM32F4x1