The Raspberry Pi Pico has been released. A £5 microcontroller board that can be used with GPIO accessories. You can program the board using MicroPython. You can connect it to a PC and it behaves like a memory stick so you can simply copy over the code easily.
Microcontroller vs computer
Most Raspberry Pi computers are single board computers that needs a complete operating system to work. Since computers are designed to run loads of programs at the same time, they need lots of memory and faster processors that draw a lot of power.
A microcontroller runs a set program for a set task in a loop, so it can run much slower and use a lot less memory and draw a fraction of the power.