ERC is an Internet Relay Chat (IRC) client built into Emacs.

Basic setup

ERC
Description	IRC in Emacs
Author	name of author
Maintainer	name of maintainer
Source	http://savannah.gnu.org/projects/erc/
Part of Emacs	yes, since 22.1

(eval-after-load "erc"
  '(progn

     ;; Set personal information
     (set 'erc-nick "defaultnick")
     (set 'erc-user-full-name "My Full Name")))

Start ERC using M-x erc or M-x erc-tls if you want to connect over SSL.

Helpful keybindings