Try this:
import threadpool, osproc
let a = spawn execProcess("ls -la .")
let b = spawn execProcess("echo $HOME")
let c = spawn execProcess("./my_other_script")
# wait for all the threads to finish
sync()
# the carrot gets the value out of the FlowVar
echo ^a
echo ^b
echo ^c
RunexecCmdEx currently doesn't work with spawn... possibly a bug. :-) But for basic use, this should do what you want.
