Comment by somat

openrsync is a neat story, it was made because they wanted to use rsync in the rpki system, but the standards body balked, saying they should not be using something where the standard was the implementation, so the openbsd folk(specifically Kristaps Dzonsons) stepped up and made a second rsync implementation so that the standards body could accept the protocol.

http://man.openbsd.org/rpki-client