There was a discussion recently about macOS Serious changing the default implementation of rsync to OpenRsync.

https://news.ycombinator.com/item?id=43605003

I posted a comment regarding Mike Bombich's "Carbon Copy Cloner", which at least started as a GUI wrapper around an rsync that's been patched to handle Mac extended attributes and related features that date from the Classic MacOS era.

Carbon Copy Cloner is commercial software, but Bombich released his patches to rsync as open source.

My comment has some links to historical context of his work.

https://news.ycombinator.com/item?id=43606281

Maybe of interest here.