At one point there were only two web browsers in the world, one was Mosaic (Mozilla is short for Mosaic Killer) and one was W3 (the emacs web browser).
* Email (gnus)
* NNTP (gnus)
* IRC
Come to mind offhand.
It's a surprisingly nice experience. You can really easily pull archives, nntp clients tend to handle threading well, etc.
I really prefer the keyboard navigation and all the niceties offered by Thunderbird than the web groups interface, each with its own set of allowed actions, mostly without keyboard navigation.
http://www.informatimago.com/linux/emacs-on-user-mode-linux....
There was a project to integrate webkit into an emacs browser mode but not sure where that stands.
w3m is an external program, which Emacs has a wrapper for http://www.emacswiki.org/emacs/w3m