LyX is an advanced document processor for Unix. It encourages an approach to writing based on the structure of your documents, not their appearance, allowing you to concentrate on writing rather than visual layout. It automates formatting according to predefined rule sets, yielding consistency throughout even the most complex documents.

LyX is a WYSIWYM document preparing program. It is like a word processor, only far better.

An What You See is What You Mean document editor for the X environment, http://www.lyx.org