Portsnap is a system written by Colin Percival for secure distribution of compressed, digitally signed snapshots of the FreeBSD ports tree.
From FreeBSD 6 through 13 (as well as 5.5), portsnap was a part of the base system.
It's a standalone program which can be run manually or in a cron job.
Its advantages include: Another alternative to cvsup is CVSync (used to manage the OpenBSD source tree), it shares cvsup disadvantages, though.
The portsnap package is distributed under the 2-clause BSD license.