Wikipedia
BlueGriffon is a WYSIWYG content editor for the World Wide Web. It is based on the discontinued Nvu editor, which in turn is based on the Composer component of the Mozilla Application Suite. Powered by Gecko, the rendering engine of Firefox, it can edit Web pages in conformance to Web Standards. It runs on Mac OS X, Windows and Linux.
BlueGriffon complies with the W3C's web standards. It can create and edit pages in accordance to HTML 4, XHTML 1.1, HTML 5 and XHTML 5. It supports CSS 2.1 and all parts of CSS 3 already implemented by Gecko. BlueGriffon also includes SVG-edit, an XUL-based editor for SVG that is originally distributed as an add-on to Firefox and was adapted to BlueGriffon.
A version without the CSS Stylesheet editor is free to download (current stable version is 1.8) and is available on Windows, Mac OS X and Linux.
Many enhancements are available via add-ons. Most add-ons such as 'Project Manager', 'CSS Stylesheet editor', 'MathML Editor', 'Word Count' and 'FullScreen view/edit' must be paid for, while only two ('FireFTP' and 'Dictionaries') are free to download.