The biggest difference between runwhen and other schedulers is that
runwhen doesn't have a single daemon overseeing multiple jobs.
The runwhen tools essentially act as a glorified sleep command.
Perhaps runwhen does nothing that at(1) doesn't, and there are
lots of things at(1) does that runwhen doesn't:

- runwhen doesn't change user IDs - thus it will never run
  anything as the wrong user.
- It doesn't keep a central daemon running at all times -
  thus it won't break if that daemon dies.
- It doesn't require any modifications to the system boot procedure.
- It doesn't log through syslog(3) - thus it won't make a mess
  on the console if syslogd(1) isn't running.
- It doesn't centralize storage of scheduled jobs (or any other
  per-job information) - thus unprivileged users can install and use it
  without cooperation from root, and without the use of a setuid program
  to handle changes.
- It doesn't send output through mail - thus it doesn't break
  if there is no mail system installed.
- It doesn't check access control files - thus it doesn't gratuitously
  deny users.