If you are an Internet Relay Chat [1] user, you can enjoy a multi-user, Scala-related chat on the Scala IRC channel:
irc://irc.freenode.net/scala
In order to access the chat, you will require an IRC client, or a web-based gateway. You can find more detailed information on the Freenode IRC network on this page [2].
A very large number of IRC clients exist, most of which are available for free; you can find a list here [3]. Some examples of popular IRC clients are mIRC [4] (Windows) and XChat [5] (Unix/Windows). Firefox users can use ChatZilla [6], an IRC client for Mozilla based browsers. OS X users can use Colloquy [7].
It is also possible to connect to the #scala channel by using a web interface. One of the best ones is Mibbit [8], but unfortunately Freenode banned [9] Mibbit [10] in June 2009. Until that is resolved, the only alternative is using Freenode's own web client [11], which is unfortunately not as refined.
Links:
[1] http://en.wikipedia.org/wiki/IRC
[2] http://freenode.net/using_the_network.shtml
[3] http://en.wikipedia.org/wiki/List_of_IRC_clients
[4] http://www.mirc.com/
[5] http://www.xchat.org/
[6] http://www.mozilla.org/projects/rt-messaging/chatzilla/
[7] http://colloquy.info/
[8] http://www.mibbit.com/?server=irc.freenode.net&channel=#scala
[9] http://blog.freenode.net/2009/06/new-freenode-webchat-and-why-to-use-it/
[10] http://blog.mibbit.com/?p=306
[11] http://webchat.freenode.net/?randomnick=1&channels=scala&prompt=1