Definitely can use across computers using a cloud sync provider (dropbox, etc).

You can also have multiple vaults, and if you want to collaborate, you can share that vault with someone.

Realtime collaboration may be a bit dangerous with syncing over a cloud provider. They are also planning a subscription with note hosting - perhaps that will include some form of collaboration.

If you put all of your GH wiki pages into a single vault, that may be a solution (though I don't think it's possible to create a solution to your setup in the most general setting - you'd have to be able to link to any file on your OS).

But you can throw your data up on a server and make it accessible from anywhere with an internet connection