Whizzywig is easy. It lets people create rich, formatted text through a web form. It actually creates xhtml, if you but you need no HTML knowledge to use it. If you can use a word processor or email, then you can use this.
Whizzywig is cross-browser: it is written in Javascript, which will run in nearly all web browsers. It is lightweight, at 25k, and is the most powerful rich text editor for its size. It does not require a Javascript library, and works independently of JQuery, MooTools, etc.
Whizzywig is FREE. Free to copy, free to use and free to change. Free for personal use, free for commercial use. See the licence for the details. Basically, it says it is FREE.