[teraflop]

Similar story here. I remember getting my first exposure to embedded development at a relatively young age through brickOS (https://brickos.sourceforge.net/), which was a complete replacement operating system for the original Mindstorms RCX (predating the NXT).

That version of the hardware was so old that it didn't even have non-volatile storage. Every time you changed the batteries, it would boot into a minimal ROM bootloader which was just powerful enough to download the rest of the firmware into RAM, via an infrared connection to your PC. That had the nice side effect of making the RCX very hacker-friendly, because it was almost impossible to permanently "brick" it (ha!).