Well, it would be very easy to make a realtime 4chan-like thing with Nchan, but it's far from the only use case. It's a general-purpose server and pubsub proxy.

The name is a play on nginx and channels. I got tired of saying "nginx http push module" all the time and renamed it.

pub/sub is a common paradigm for describing certain types of event systems or message queues.

Clients can subscribe to "channels" and they will receive all messages "published" on those channels.