Unison was the first thing I tried after moving away from DropBox. The main problem I had with it was that both machines involved in the syncing had to be running which made moving from laptop to desktop not as seamless as I would have liked. Still the syncing process was flawless. I had better results using Seafile, http://seafile.com/en/home/, their free account was sufficient for my needs and worked great. You can self-host if you are worried about keeping control of your files.

You'll have that problem with anything you don't run yourself so that seems like an unfair complaint. Can't this sync desktop <-> server and laptop <> server?

I ran unison for a while but the conflict resolution was unfortunately lacking. It repeatedly stopped sync'ing properly until I intervened manually.

A few months ago I switched to csync[1], which looks better so far.

[1] https://www.csync.org/

The last csync release is from August 2013. Is the project still alive?

I don't know. It simply works for me ever since I installed it (on linux and OSX) so I never bothered to check for updates.

In Seafile the server doesn't notify changes to clients, instead the clients poll every 30 seconds, which means that changes are synced with a 30 second delay (and presumably bandwidth is wasted). See https://github.com/haiwen/seafile/issues/992. I'm not a fan of Dropbox but at least the lag is only a few seconds, which I think is because the clients notice changes with inotify and send them to the server, and the server probably pushes updates to the clients.

I haven't tried to use it seriously, but seeing that it doesn't do this right discourages me a bit from testing it further.

Nice! I hadn't heard of Unison.