The Shoutbox is a module that can be placed in either column of Tiki. It serves as a site-wide Instant Messaging service. Shoutbox is very useful as a means for site participants to communicate with each other.
Tikiwiki has its own internal postal service that does not require users to disclose their email.
Want to get a word out to your whole subscriber base? Tiki does that.
Want to set up internal chat boards? Tiki does that too.
Want to add an rss feed as content into your site - easily done.
You can request, post and edit wiki pages by email - how cool is that.