Open Source Online HTML Editor: Xinha
Xinha is a powerful & open source HTML (WYSIWYG) editor that works in all current browsers. Its configurabilty and extensibility make it easy to build just the right editor for multiple purposes, from a restricted mini-editor for one database field to a full-fledged website editor. Its liberal, BSD licence makes it an ideal candidate for integration into any kind of project.
It is a community-built script presenting various options for max. customization.