So there's a working Linux build (sort-of).

The Client works fine - but launching the server via the "Host Game" button doesn't work. You can work around it by launching Gravity.Server.bin.x86_64 within the game files directory, or by connecting to a friend's Windows machine :)

When I can find a spare keyboard I'll work on getting the OSX build up and running - hopefully now that Linux is mostly sorted it'll be an easier task.