XEmacs – a highly customizable open source text editor and application development system.
It is licensed under the GNU Public License and related to other versions of Emacs, in particular GNU Emacs. Its emphasis is on modern graphical user interface support and an open software development model, similar to Linux. XEmacs runs on Windows 95 and NT, Linux and nearly every other version of Unix in existence. Support for XEmacs was supplied by Sun Microsystems, University of Illinois, Lucid, ETL/Electrotechnical Laboratory, Amdahl Corporation, BeOpen, and others, as well as the unpaid time of a great number of individual developers.
An alternative to GNU Emacs, XEmacs was originally based on an early alpha version of FSF’s version 19, and has diverged quite a bit since then. XEmacs was known as Lucid Emacs through version 19.10. Almost all features of GNU Emacs are supported in XEmacs. The maintainers of XEmacs actively track changes to GNU Emacs while also working to add new features.