BibSync is tool (a separated software right now, but can be transformed in a plug-in) aimed to transmit (synchronize more or less like rsync) database entries and the associated files to a server. Basically, it allows to share the database (like BibSonomy) but also the associated files (like no other software that I knew about).
The software is in beta test. If some one are interested I can publish it, but right now I don't know how. So, if some one have an idea please let me know. By the way, sorry to post it here. I seemed to me that this was the right place, but I am not sure.
The tool you mentioned is NOT https://github.com/minad/bibsync, but something different?