LyX - A WYSIWYM document processor.

LyX is a document processor that encourages an approach to 
writing based on the structure of your documents (WYSIWYM) 
and not simply their appearance (WYSIWYG).

LyX combines the power and flexibility of TeX/LaTeX with the 
ease of use of a graphical interface.
This results in world-class support for creation of mathematical 
content (via a fully integrated equation editor) and structured 
documents like academic articles, theses, and books.