I once gave git-annex a serious try (a few weekends of all-day efforts), as a way of sharing my music library between personal machines. It seemed to fail pretty hard on the cross-platform part. I really wanted it to work, I just couldn't get it to do so.

It was great at first on a single Linux machine, but once I had to support Windows, things became much more complicated. Most of this I attribute to Windows - different filename character restrictions, no usable symlinks, git only kinda-sorta supported through cygwin. Setting up an SSH server under Windows was something I didn't want to do, and HTTP sync was pretty buggy (different hashing schemes between the two computers, for some reason).

If things have gotten better, or someone's written a good tutorial on having an actual decentralized repo shared between Windows and Linux machines, I'd be interested in giving it another go. Also might need to hack up a mobile app.

I haven't dug into Syncthing's protocol yet, but I also like the idea of being able to easily share a single sync'd folder or file with an outside person, but not having to point them at a full repository.

This is a year or so old, but it still works for new customers:

http://www.rsync.net/products/git-annex-pricing.html

Can you explain to me why and how I would use git-annex for real time sync? From what I understand of it, it works well for backups and for managing media files, but I don't understand how it handles the use case of making two directories on two computers pretend to be one.