I'm actually hacking right now on a personal project that might be relevant. It eschews the 'sync' metaphor and focuses more on the 'share' metaphor, though - i

I'm actually hacking right now on a personal project that might be relevant. It eschews the 'sync' metaphor and focuses more on the 'share' metaphor, though - it is not so useful for files that change frequently, but pretty robust for sharing arbitrary sets of files or data between a group of users. (It will also include user and access management). The whole thing currently sits on top of BitTorrent although I suspect I'll end up writing a forked implementation at some point to support some extensions I'm working on. Active, dynamic syncing is great for some kind of data but not so important for others, and I feel like that's the hurdle that needs to be overcome. More interesting to me is painless, fast, robust, and configurable sharing of relatively static data. (Some versioning may be included but it won't be a first-class system.)