cron.  When ISC cron 5.0 is out the integration will be even tighter.
Also rename /var/cron/{allow,deny} -> /var/cron/cron.{allow,deny}
for consistency with POSIX and at.{allow,deny} and install an empty
cron.deny file (as we do at.deny) since crontab will require this
in the near future for POSIX compliance.
After a "make build" you can update your system as follows:
# mv /var/at/* /var/cron
# mv /var/cron/jobs /var/cron/atjobs
# mv /var/cron.allow /var/cron/cron.allow
# mv /var/cron.deny /var/cron/cron.deny
# rm -rf /var/at
# kill `cat /var/run/cron.pid` ; cron