BT Sync Resilio or Syncthing which I haven't tried.

Uses Bittorrent Protocol, so your school network admin may block it, but it's not cloud hosted, so if you need to access files on one computer that's not on another, you can't cloud retreive it.

I like BT Sync because I can sync any folder, any size, anywhere on the hard drive. I'm not limited to one folder like dropbox.

Only downside is that there's no cloud, so if I do something on computer a, and don't sync on computer B before I leave the house, there's not guarantee that the file will be on computer B, because not all public/work networks will allow torrenting protocols which this file sharing system works on. Of which, if I'm on the go on computer b, there's no guarantee that if it gets stolen, any files worked on it will be transferred to computer a. And of course, when I get home, I have to turn on computer B so that it can update to computer A