Clon is a Common Lisp library for scheduling much like cron.

It's under the MIT licence. See COPYING.

How to use it:

;;; create a stateless schedule:
(make-typed-cron-schedule :second '(member 0 10 20 30 40 50))
;;; create a scheduler that remembers the last scheduled time:
(make-scheduler *)
;;; schedule a function:
(schedule-function (lambda ()
                    (print (get-universal-time)))
                   *)
;;; unschedule the timer returned by SCHEDULE-FUNCTION:
(trivial-timers:unschedule-timer *)