I tried few Rich Text Editors like FCKeditor or TinyMCE, they helped but they have some anomalies, they add extra html code and sometimes you just want more quality.
The 37signals announced new open source JavaScript rich text editor based on WYSIWYG JavaScript framework called WysiHat. This is very early developer release, and it provides extensible foundation to design your own design for text editor. Witth few lines of code, we can run the WysiHat editor. The 37signas let us the customize it by our need, so this is for developers who want to develop own rich editor, and WysiHat can be groundwork.
They will continue to develop this WysiHat, and they call developers to check out the project and give the feedback to them.
Read 37signals announcement about WysiHat.