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:

http://www.clisp.org/impnotes/mt.html