A true symmetric multi-processing (SMP) RTOS for the ARM Cortex A series (32 & 64 bits) and Cortex M3/M4.
Abassi multicore is available in two versions: mAbassi is the full feature RTOS and µAbassi is a strip-down version. mAbassi requires only around 6 Kbytes of code with all features enable (details).
Both versions are available as freeware (Download).
A feature highlight comparison table between mAbassi and μAbassi is available here.