FreeRTOS.org is an open source mini real time kernel. V3.2.4 is the first version to include a port for the Microblaze. See
There are many existing ports, but this is my first venture into the FPGA world. As I am new to soft processors and FPGA's I might not have everything set up in the most efficient fashion - but the port has been working well on soak test for many days now.
Hope it might be of interest to some (?).
Regards, Richard.