IRC is one of the primary communication tools for Wikipedia and its sister projects. The community is so distributed, coordinating meetings using UTC time becomes second nature.

There are dozens and dozens of channels. This page attempts to track just some of them.

http://meta.wikimedia.org/wiki/IRC/Channels

And even the non-technical staffers at the Wikimedia Foundation hold "office hours" on IRC from time to time.

http://meta.wikimedia.org/wiki/IRC_office_hours