Do you have an old PC lying around gathering dust? How about a small-capacity USB flash drive sitting, unloved in a drawer? You can reuse your old computer and a USB flash drive by installing a tiny Linux distribution.
Mini Linux distros are great as they require fewer system resources than other options yet still deliver a whole operating system experience, and we have nine of the smallest Linux distros for you to choose from.
I’ve programmed Arduinos and microcontrollers, including one with an ARM Cortex M4 CPU. In all cases, I just write C code on my computer and download it onto the board with a USB cable. No OS needed.