WaitNext

WaitNext[{eid1,eid2,…}] waits until the first evaluation represented by any of the eidi finishes, then returns its result, the corresponding eidi, and the list of remaining eidk. 

WaitNext[{eid1,eid2,…},h] wraps the head h around the result before returning it.

Please visit the official Wolfram Language Reference for more details and examples on core symbols.