Internet Relay Chat (IRC) is instant messaging focused around topics rather than people, and requires no registration. The Wagn channel is #wagn on irc.freenode.net.
There's a web interface offered by freenode.net which you can use via this form:
If you have an IRC client, just click: irc://irc.freenode.net/wagn. Downloading a client is a little more complicated than the web chat above, but will offer more features. Some recommendations for different systems:
Read this for tips on why IRC is worth figuring out. For the more adventuresome, here is the IRC Help Archive. Wikipedia's IRC page is pretty technical.