What is LyX?
LyX is the first WYSIWYM document processor.
Ehhh... please explain.
LyX is a document processor that encourages an approach to writing based on the structure of your documents, not their appearance. It is released under a Free Software / Open Source license.
LyX is for people that write and want their writing to look great, right out of the box. No more endless tinkering with formatting details, 'finger painting' font attributes or futzing around with page boundaries. You just write. In the background, Prof. Knuth's legendary TeX typesetting engine makes you look good.
On screen, LyX looks like any word processor; its printed output -- or richly cross-referenced PDF, just as readily produced -- looks like nothing else. Gone are the days of industrially bland .docs, all looking similarly not-quite-right, yet coming out unpredictably different on different printer drivers. Gone are the crashes 'eating' your dissertation the evening before going to press.
LyX is stable and fully featured. It is a multi-platform, fully internationalized application running natively on Unix/Linux and the Macintosh and modern Windows platforms.