I just uploaded a small library to github (and clojars), It’s a generalisation of what I use for recurrent tasks in my clojure programs, the fact that the recent pragprog article had a handrolled version of it too convinced me it was worth putting together in a lib.
The library provides an easy mechanism to register process for later execution, either recurrent or ponctual. It is called TRON, replacing CRON’s C which stands for command - as in: command run on - with a T for task.
Here is a short excerpt of what it can do:
(ns sandbox (:require tron)) (defn- periodic  (println "periodic")) (defn- ponctual  (println "ponctual")) ;; Run the fonction 10 seconds from now (tron/once ponctual 10000) ;; Run the periodic function every second (tron/periodically :foo periodic 1000) ;; Cancel the periodic run 5 seconds from now (tron/once #(tron/cancel :foo) 5000)
The code is hosted on github: https://github.com/pyr/tron, the full annotated source can be found here and the artifacts are already on clojars (see here). The library still needs a better way of expressing delays which will be worked on, and might benefit from macros allowing you to embed the body to be executed later. All in due time.