An IRC client. Preferably used in conjuection with screen
screen -S irc irssi will give you a named screen session called <somePid>.irc, so later, when you have detached your screen (
C^a d), logged off, done other things, come back, and want to resume your session, you could just do
screen -ls and get a listing of all your currently running screens, followed by
screen -d -r <somePid>.irc, and you are back where you left off.