XEmacs is a self-documenting, customizable, extensible real-time
display editor.

Users new to XEmacs will be able to use basic features fairly rapidly
by studying the tutorial and using the self-documentation features.
XEmacs also has an extensive interactive manual browser.  It is easily
extensible since its editing commands are written in Lisp.

XEmacs's many special packages handle mail reading (RMail) and sending
(Mail), outline editing (Outline), compiling (Compile), running
subshells within Emacs windows (Shell), running a Lisp read-eval-print
loop (Lisp-Interaction-Mode), automated psychotherapy (Doctor :-) and
many more. There is a WWW browsing mode written fully in elisp
that looks and behaves much like the netscape WWW browser.

XEmacs has similar functionality to GNU Emacs. It uses a different 
display model, including support for Motif menu and scroll bars and the
ability to run as a widget inside other applications. Many people say
it looks nicer than GNU Emacs.

WWW: http://www.xemacs.org