What is ZNC?
znc is an IRC proxy. It runs as a daemon and connects to IRC server, then allows you to connect from a workstation and work as the user that is logged in to the IRC server. After you disconnect, it maintains the connection to the server. It acts like any normal IRC server, so you can use any IRC client to connect to it.
Some of its features include support for multiple users, multiple clients, and multiple IRC servers; playback buffers to catch up with what happened while you were detached, SSL encryption, DCC proxying, and a plugin interface with many plugins supporting other features.