90:  What is the difference between Emacs and XEmacs (formerly "Lucid
     Emacs")?

  First of all, they're both GNU Emacs.  XEmacs is just as much a later
  version of GNU Emacs 18 as the FSF-distributed version.  This FAQ refers
  to the latest version to be distributed by the FSF as "Emacs," partly
  because the XEmacs maintainers now refer to their product using the
  "XEmacs" name, and partly because there isn't any accurate way to
  differentiate between the two without getting mired in paragraphs of
  legalese and history.

  XEmacs, which began life as Lucid Emacs, is based on an early version of
  Emacs 19 and Epoch, an X-aware version of Emacs 18.

  Emacs (i.e., the version distributed by the FSF) has a larger installed
  base and supports character terminals, while XEmacs can do some clever
  tricks with X Windows, such as putting arbitrary graphics in a buffer.
  Emacs and XEmacs each come with Lisp packages that are lacking in the
  other; RMS says that the FSF would include more packages that come with
  XEmacs, but that the XEmacs maintainers don't always keep track of the
  authors of contributed code, which makes it impossible for the FSF to
  have certain legal papers signed.  (Without these legal papers, the FSF
  will not distribute Lisp packages with Emacs.)
 
  Many XEmacs features have found their way into recent versions of Emacs,
  and more features can be expected in the future, but there are still many
  differences between the two packages.

  The latest version of XEmacs as of this writing is 19.11; you can get it
  at

    ftp://ftp.cs.uiuc.edu/pub/xemacs/xemacs-19.11.tar.gz

  More information about XEmacs, including a list of frequently asked
  questions (FAQ), is available at

    http://xemacs.cs.uiuc.edu/