zfs-auto-snapshot:

An alternative implementation of the zfs-auto-snapshot service for Linux
that is compatible with zfs-linux and zfs-fuse.

Automatically create, rotate, and destroy periodic ZFS snapshots. This is
the utility that creates the @zfs-auto-snap snapshots if it is installed.
For this version, the different labels (e.g. frequent, hourly, daily, 
weekly, monthly) are applied as the zfs property 
com.sun:auto-snapshot-label.

This program is a posixly correct bourne shell script.  It depends only on
the zfs utilities and cron, and can run in the bash shell.  It has been 
adapted slightly to run under FreeBSD, but aside from the location of
bash itself and of getopt, it should work on other systems.