A library called SCHEDULER (Arduino - Scheduler) can be found in the ARDUINO site.
It simply has startLoop() and yield() methods... nothing more.
The site claims it might not change in the near future... and consider the library "under construction".
This might be for single-core boards (backward compatible with uno)
I don't know if this library is the "best" currently. because DUE and GALILEO have a more powerful (multicore) processor.
It will be good if INTEL will create 'advance' libraries, run some hardware performance testing against GALILEO, and contribute to the Arduino community.
What can we do with GALILEO that we cannot do with the multi-core boards of the competing vendors?