Replying to
@fogti@chaos.social @gsuberland@chaos.social @jackemled@furry.engineer @viq@social.hackerspace.pl @zl2tod@mastodon.online @hailey@hails.org Most alternative rsync implementations are stuck on the simpler protocol version 27, which is before many improvements such as the generation of the file list in parallel: https://github.com/gokrazy/rsync#existing-rsync-implementation-survey
Instead of trying to reimplement the undocumented rsync protocol, I would rather wish for an active community around a modern alternative file transfer tool based on content-defined chunking (as used by restic and borg backup). Google had a proof-of-concept with benchmarks for Stadia, but abandoned it: https://github.com/google/cdc-file-transfer
Following the ideas of FastCDC, resync looks promising on redefining the protocol, while keeping the command line interface familiar to users of rsync: https://github.com/vedLinuxian/resync-rs