cvsup is an excellent program, allowing retrievals of file revisions from a cvsup server.  It’s been traditionally used in FreeBSD and DragonFly to get updates to the system source…  However, cvsup requires a working version of Modula-3 to build, and the C-based replacement, csup, can’t run as a server.  Rsync is a common alternative that also offers good performance.

I did a comparison of the two, repeatedly running partial and full downloads from a DragonFly mirror that supplied the same data via both protocols.  I posted the results, and dragonflybsd.org is now offering files via rsync.