It is an open source, wysiwyg, Web authoring system. The Guide is written in the hope that it will both prove useful for new users and act as a reference guide for those more experienced. It is built on the work of the Nvu (pronounced N-view) Open Source Project..
There are some of their features
File Management and FTP Capable
KompoZer has a built-in file management tool that allows you to maintain your website, including a page-heavy ecommerce operation, publishing updates in just a click, and moving files back and forth from the server via file transfer protocol (FTP). This is an especially useful feature for managing large sites or sites that are frequently updated. For example, if you are frequently changing merchandising zones or a deal of the day section (as Jay Shaffer of Infopia recently suggested in a webinar), you can easily make your updates with KompoZer without employing a separate FTP tool.
Tabbed Document View
For someone new to XHTML (extensible hypertext markup language), CSS (cascading style sheets), or other web languages, KompoZer can be a lifesaver. The tool's WYSIWYG editor works like a word processor. A non-technical designer can type just like she was writing a letter, paste in images, color text, and generally create a web page without coding a single character.
You could even use KompoZer to learn XHTML, toggling between the design view and the underlying code.
SOurce :- PeC Review
For Windows user, don't worry there are windows version for us..
I've used it .It is easy to use especially for basic website . Just try yourself and download for free at kompozer.com