I tend to avoid using an RTOS on smallish MCUs (<128KB worth of firmware) since they can create as many problems as they solve, but in the ‘just for the heck of it’ department, I was really impressed when I stumbled across this custom RTOS that can run on the itsy bitsy 4KB flash, 1KB SRAM DIP-8 LPC810 MCU from NXP.  It’s a challenge to fit printf, UART and a bit of logic on this thing already, but if you want some real street cred, you can one up every other kid on the block by doing it with an RTOS!  Great job on this.  Interested in trying it out yourself?  Adafruit has a small LPC810 kit with everything you need!