http://www.seamonkey-project.org/

http://www.aptana.org/

    The professional, open source development tool for the open web
    It's ready. It's time. Develop and test your entire web application using a single environment. 
    With support for the latest browser technology specs such as HTML5, CSS3, JavaScript, Ruby, Rails, 
    PHP and Python. We've got you covered!

http://www.arachnoid.com/arachnophilia/index.php

    Arachnophilia 5.5 greatly improves the text editing / syntax coloring scheme and the number of supported file types. 
    It also introduces two new beautification (code formatting) engines, for Ruby programs and and Bash shell scripts.
    Arachnophilia 5.4 introduces support for international characters and content, a feature described more fully here.
    Arachnophilia 5.3 has a new feature called "HTML Validate" that will help you find and correct structural errors in 
    your pages. In essence, this feature takes your page apart, tells you what it finds, and allows you to navigate your  
    page in a hierarchical sense, identifying areas for improvement.

http://bluefish.openoffice.nl/features.html

    This I tried and liked for the cport project

http://www.kompozer.net/

http://quanta.kdewebdev.org/viewscreenshot.php?id=7&application=quanta

http://www.w3.org/Amaya/