It's actually something I've been working on that I want to put up on github. I hacked up a Python version of it as a proof-of-concept but rewrote it in C as an installable executable using autotools.

Basically I tell it which directory I want it to watch for changes and it does automatic syncing by piping rsync. I keep a local and remote signature of the files and their timestamps. When it first starts up, it pulls the server sig file and compares it to the local one. If there's a mismatch, the server is updated. From there it manages the signatures locally until they're different.

Writing the sig file to the remote server is done in the same rsync pass because it's stored in the local directory as a dotfile.

I realize rsync does its own checksums, but using my own crude signature files makes it so I don't have to keep calling rsync. I only call it when something changes.

I also have some stuff I'm working on that ties into auto-restarting servers when syncing finishes, rolling server deployments for no downtime, db migrations, etc.