Femto OS

Femto OS: RTOS for small MCU’s like AVR.

Round Robin Scheduling. Every task in the each priority gets an equal amount of time.
Preemptive and cooperative. Choose between preemptive or cooperative on a task by task basis.
Shared Stacks for tasks. Possibility to save ram by letting tasks share their stack space.
Register Compression. Save only the registers that are used on the stack at taskswitch.
Separate OS/ISR Stack Space. The OS (ISR) has its own stack space
Power save on Idle. The idle task can be used to save power.
Honest Time Slicing. Every task gets the same amount of execution time, so no starvation.
OS interruptible. Large parts of the OS can be made interruptable.
Resource Tracking. Tasks that are terminated are managed to release all kernel resources.

ATMega328P-OperatingSystem. A very small operating system for the Atmel ATMega328P providing basic task switching.