NeatHTML.com is a PHP based website used to neatify, view, and edit HTML source code directly from a web-browser. The site was created initially for personal use, to allow for automated source code beautification for some web-development projects. It was later modified to work online, and can now be used by anyone completely free.
The site now uses ACE Editor as the source syntax highlighter. Ace Editor supports the use of editor options, settings, and even themes! all directly from the web-browser, and completely free.
You can try it for yourself here. This site is now abandoned to focus on larger projects.
The project was completed in December 2012, and is under continuous development.