I'm running Clozure CL on quadcore ARM-based computers at home. Nicely multithreaded. Works great.
Threads in ECL:
http://ecls.sourceforge.net/new-manual/ch27.html
Threads in Clozure CL:
http://ccl.clozure.com/manual/chapter7.html#Programming-with...
Threads in SBCL:
http://www.sbcl.org/manual/index.html#Threading
ABCL support threads.
Threads in CLISP:
My knowledge is pretty much limited to the free Common Lisp implementations, since I never had a budget for a commercial one, and their threading story has not been so happy. But that's not a valid criticism of Common Lisp.