LÖVE

Is there any official built-in socket/networking/multiplayer support?

Or are we stuck with programming that from scratch?

I did see something called LUBE in the forum somewhere that is user-created

The module LuaSocket comes prebundled with LÖVE. Implementing multiplayer support with LuaSocket is something that you have to do on your own, however. LUBE is a module created to simplify this process. There should be a multiplayer demo in time.