… and Guile has SRFI-18 support.
It might be good to also tabulate which Schemes have thread support, even if not SRFI 18, like ChezScheme and Racket.
MIT Scheme has had threading support since the early 1990s, but it has never been documented in the manual. It works well, though. I use it in my web server, for example. Here are all the bindings that contain the string "thread":
assert-thread-mutex-owned
condition-type:derived-thread-error
condition-type:no-current-thread
condition-type:thread-control-error
condition-type:thread-dead
condition-type:thread-deadlock
condition-type:thread-detached
condition-type:thread-error
condition/derived-thread?
create-thread-continuation
deregister-io-thread-event
permanently-register-io-thread-event
set-thread-timer-interval!
stack-frame/block-thread-events?
textual-port-thread-mutex
thread-queue/dequeue-no-hang!
thread-queue/peek-no-hang
thread-queue/queue-no-hang!
unlock-thread-mutex-and-wait
with-create-thread-continuation
with-thread-events-blocked
with-thread-mutex-try-lock
with-thread-mutex-unlocked
with-thread-timer-stopped
without-thread-mutex-lock
;Unspecified return value