LyX

Advanced open source document processor

Alongside Kile, LyX is another tremendous powerful LaTeX GUI. It allows you to create impressive documents in HTML, PS or PDF format rendered with unbeatably beautiful Computer Modern fonts. LyX is also available for Windows and is a little less difficult to use, in my opinion. I have reviewed LyX not that long ago.  

User-friendly LaTeX source editor and TeX shell and KDE.

LyX - Word processor.

LyX is an advanced open source document processor that encourages an approach to writing based on the structure of your documents, not their appearance. LyX lets you concentrate on writing, leaving details of visual layout to the software. LyX runs on many Unix platforms (including MacOS X), OS/2, and under Windows/Cygwin. Note that all these ports use the same xforms interface and therefore need an X server. LyX produces high quality, professional output -- using LaTeX, an industrial strength typesetting engine, in the background; LyX is far more than a front-end to LaTeX, however. No knowledge of LaTeX is necessary to use LyX, although it will give a user more power. LyX is stable and fully featured. It has been used for documents as large as a thesis, or as small as a business letter. Despite its simple GUI interface (available in many languages), it supports tables, figures, and hyperlinked cross-references, and has a best-of-breed math editor.