STM32F103C8T6 ARM STM32 Minimum System Development Board, commonly referred to as the "Blue Pill" board.
Powerful ARM Cortex MCU Microcontroller chip clocked at 72MHz Can be flashed with an Ard-uino-compatible bootloader.
For details, search for "stm32duino blue pill", also see "stm32duino" and mentions on Hackaday
Includes ST-Link V2 programmer (random color and markings - most are gray, blue, brown/gold, or green)