We developed a coroutine-based event-driven networking lib in Lua (not open sourced yet, but it looks like it might change someday). One of the neat thing is that we're able to run that on tiny ARM-based embedded hardware.

I think there are people who did similar stuff for classic PC hardware, and already open-sourced their work; you might want to look at nmap, among others.

The external API is a superset of Luasocket's, so the event loop can remain completely transparent for users if they choose so. Proper coroutine support really rocks!