Finally got around to trying Syncany last night.
1. It's a command-line, not GUI.
2. Currently has plugins for FTP, SFTP, WebDAV, Local and Amazon S3
3. I got it to connect to my Box account VIA WebDAV, but it didn't sync anything from my Box.com folder, though it did upload it's own database folders and stuff.
Well, it's Alpha, what can I say?