WYSIWYG editors are a key feature in most CMS products: both commercial and open source. These components add HTML controls to a web form field so that a non-technical user can apply their own formatting to the text that they enter. I think of WYSIWYG editors as being The Great Compromise of content management. WYSIWYG editors balance the needs of the authors, who would rather use something like MS Word to enhance their prose with formatting, and systems people who want structured data to store and reuse.
A couple of weeks ago I was setting up Bricolage to work with htmlArea (which is integrated with Bricolage and several other open source CMS) and was surprised to see that the latest version (3.0) was no longer available on the htmlArea website. I learned from the list that InteractiveTools is no longer maintaining the code and the project has moved to DynArch.com (thanks, Bret Dawson for the answers).
If you want a list of HTML Editors and the the browsers they support, check out the HTMLArea website.