Kupu is a client-side WYSIWYG editor written in JavaScript. It’s a feature-complete authoring tool that allows users to easily manage (X)HTML content in a familiar user interface. Kupu works on both IE based browsers (IE 5.5+) as well as Mozilla variants (Mozilla 1.3.1+). It’s server-independent (will work from the filesystem), extensible using a simple but powerful plugin API and is highly configurable. It supports saving using both POST (where Kupu becomes part of a form) and PUT (where the code will issue an asynchronous HTTP call to the server) and can be used multiple times on the same page. Kupu is easy to extend and has a flexible templating system allowing different setups to be generated from the same XML files. Plugins can be downloaded separately from the core. Kupu's BSD-style license allows it to be used in any type of project. Kupu is integrated into many systems, including CMS’s such as Apache Lenya, Silva, Plone and Magnolia, as well as applications like Twiki.

Features:

100% JavaScript.
Simple but powerful API.
Works on both IE and Mozilla based browsers.
Can be integrated into any type of HTTP server.
Can use either POST or PUT.
Extensible using plugin architecture.
Customizable: CSS for layout, XML for config, extensible using JavaScript. Provides tag filter to guarantee compatible markup and well-formed data. Broad user base: integrated in many open source and proprietary projects. Very friendly and helpful community.