WysiHat: Open source WYSIWYG Prototype-based editor by 37signals

WysiHat is a WYSIWYG JavaScript framework that provides an extensible foundation to design your own rich text editor. WysiHat stays out of your way and leaves the UI design to you. Although WysiHat lets you get up and running with a few lines of code, the focus is on letting you customize it.

More info: WysiHat

Source:→ Ajaxian