MicroPython

British physicist Damien George funded it on Kickstarter in 2013, together with his own board, the pyboard, built around an STM32. The interpreter is written in C from the ground up rather than being a slimmed-down CPython, and it brings a garbage collector, a bytecode compiler and a REPL over the USB serial port. That last part is the point: type pin.on() and the LED lights up, no compile, link or flash cycle required.

It now runs on the ESP32, the Raspberry Pi Pico and hundreds of other boards. In 2017 Adafruit forked it into the beginner-friendly CircuitPython. The limitation is predictable: garbage collection can pause at any moment, so hard real-time work belongs in C, ideally called from Python.