Raspberry Pi Pico
The Raspberry Pi Pico is a low-cost, high-performance microcontroller board with flexible digital interfaces. It feature the RP2040 which marks Raspberry Pi's first microcontroller designed in-house. Pico provides minimal (yet flexible) external circuitry to support the RP2040 chip. The majority of the RP2040 microcontroller pins are brought to the user IO pins on the left and right edge of the board.
The Raspberry Pi foundation provides excellent documentation for programming the RP2040 using either MicroPython or C++.
More information is available on the website of Raspberry Pi.