From http://www.texmacs.org

GNU TeXmacs is a free scientific text editor, which was both inspired by TeX and GNU Emacs. The editor allows you to write structured documents via a wysiwyg (what-you-see-is-what-you-get) and user friendly interface. New styles may be created by the user. The program implements high-quality typesetting algorithms and TeX fonts, which help you to produce professionally looking documents.

The high typesetting quality still goes through for automatically generated formulas, which makes TeXmacs suitable as an interface for computer algebra systems. TeXmacs also supports the Guile/Scheme extension language, so that you may customize the interface and write your own extensions to the editor.

TeXmacs currently runs on PC's and PPC's under Gnu/linux (a >200MHz processor and >32Mb of memory are recommended) and on sun computers. Converters exist for TeX/LaTeX and they are under development for Html/MathMl/Xml. In the future, TeXmacs is planned to evolve towards a complete scientific office suite, with spreadsheet capacities, a technical drawing editor and a presentation mode.