Here is another Raspberry Pi for DIYers. The Raspberry Pi Pico is a $4 microcontroller based on a new custom chip developed by the company. It is based on the RP2040, which has a dual core ARM Cortex-M0+ @ 133MHz, 264KB on-chip RAM, 30 GPIO pins, and USB 1.1 controller. It also has a USB mass storage boot mode.
Raspberry Pi Pico has a power supply chip supporting input voltages from 1.8-5.5V. It gives you access to 26 of the 30 GPIO pins. It has a single button for changing mode at boot time.