They have apps for Windows, Mac, Linux, iOS and Android. I've been using it for about two months now with no problems.
On the other hand, it gives you a nice web-based file browser, CardDav, CalDav, and a RSS webapp. And there's a basic iPhone app.
The approach posted somewhere else in the comments[0] seems interesting. Use BTSync for the synchronization, and put ownCloud over that for the web interface and other goodies. I'm tempted to experiment with that.
[0] http://blog.bittorrent.com/2013/05/23/how-i-created-my-own-p...
A couple of days ago I installed btsync and tested syncing one 130 MB big directory. I added it both at the same time to btsync and ownCloud. After about 2 minutes btsync had its copy on the other computer. After one hour ownCloud had cpied about 50 MB to the server when I canceled it and removed the ownCloud dropbox-client from my computers.
I still use all the other stuff to synchronize my calendar/address book between my computers and mobile devises and I even use their RSS backend but with my own Firefox OS app https://marketplace.firefox.com/app/feedmonkey/
And we own the data, not Apple.
I highly recommend owncloud.
Missing from both though is a mobile version. I quite like my Elements (A text editor for Dropbox files).
> BitTorrent Sync synchronizes your files using a peer-to-peer (P2P) protocol.
https://www.dropbox.com/help/137/en
Note: Dropbox employee, but this is public information.