http://cypherpunk-handbook.i2p/articles/openbsd.html
It began as part of rpki-client(8) , which needed
to retrieve RPKI repository data using the rsync protocol, and was imported
into OpenBSD in 2019 . This gave the base system an implementation
under OpenBSD's direct integration, audit, and maintenance process and
its preferred license, without importing the original GPL rsync
code. openrsync deliberately implements a smaller interface.