Csync2 – file synchronization tool using librsync and current state databases
github.com
github.com
Have you used osync for multiple users to a shared server? A lot of sync tools seem great till you want a "star" setup where multiple clients sync against a single central location.
As I understand it csync and unison would both be "safe" in this situation, with the caveat that unison requires the same binary version at both ends, so you'll likely need multiple unison binaries on the server to support different client versions.