Source : Free On-Line Dictionary of Computing

Xemacs
     
         (Originally "Lucid Emacs") A text editor for the
        {X Window System}, based on {GNU} {Emacs} version 19, produced
        by a collaboration of {Lucid, Inc.}, {SunPro} (a division of
        {Sun Microsystems, Inc.}), and the {University of Illinois}.
     
        Lucid chose to build part of {Energize}, their {C}/{C++}
        development environment on top of GNU Emacs.  Though their
        product is commercial, the work on GNU Emacs is {free
        software}, and is useful without having to purchase the
        product.  They needed a version of Emacs with mouse-sensitive
        regions, multiple fonts, the ability to mark sections of a
        buffer as read-only, the ability to detect which parts of a
        buffer has been modified, and many other features.
     
        The existing version of {Epoch} was not sufficient; it did not
        allow arbitrary {pixmaps} and {icons} in buffers, "undo" did
        not restore changes to regions, regions did not overlap and
        merge their attributes.  Lucid spent some time in 1990 working
        on Epoch but later decided that their efforts would be better
        spent improving Emacs 19 instead.
     
        Lucid did not have time to get their changes accepted by the
        {FSF} so they released Lucid Emacs as a forked branch of
        Emacs.  Roughly a year after Lucid Emacs 19.0 was released, a
        beta version of the FSF branch of Emacs 19 was released.
        Lucid continued to develop and support Lucid Emacs, merging in
        bug fixes and new features from the FSF branch as appropriate.
     
        A compatibility package was planned to allow Epoch 4 code to
        run in Lemacs with little or no change.  (As of 19.8, Lucid
        Emacs ran a descendant of the Epoch redisplay engine.)
     
        [Update?]
     
        (2000-05-16)