From #openttdcoop wiki
IRC (Internet Relay Chat) is used to improve the communication between all players and friends of #openttdcoop.
If you want to join our community, you will need an IRC client. We therefore recommend one of these clients:
http://www.xchat.org/ (Many OS'es)
http://bersirc.free2code.net/index.php/home (Microsoft Windows Only)
http://www.hydrairc.com/ (Microsoft Windows Only)
http://www.mirc.com/ (Mircosoft Windows Only)
http://colloquy.info/ (Mac OS X)
If you installed the client, connect to the OFTC IRC network. For further details and FAQ see http://www.oftc.net/ .