If you are OK with stackful coroutines (that libmill provides) then an RTOS (like freertos) would mostly be the same thing. Context switching for those isn’t as

If you are OK with stackful coroutines (that libmill provides) then an RTOS (like freertos) would mostly be the same thing. Context switching for those isn’t as expensive as for PC Threads and processes. If you can’t afford the memory for a dedicated callstack per thread then there are the other event driven models that had been mentioned here. However one loses out one real-time capabilities and priority handling by using those compared to a preemptive RTOS.