CKEditor (formerly FCKeditor) is an open source WYSIWYG text editor from CKSource that can be used in web pages. It aims to be lightweight and requires no client-side installation. The first version was released in 2003.
Its core code is written in JavaScript, having server side interfaces with Active-FoxPro, ASP, ASP.NET, ColdFusion, Java, JavaScript, Lasso, Perl, PHP, Python. and Ruby on Rails.
CKEditor is compatible with most Internet browsers, including: Internet Explorer 6.0+ (Windows), Firefox 2.0+, Safari 3.0+, Google Chrome (Windows), Opera 9.50+, and Camino 1.0+ (Macintosh).
MediaWiki+FCKeditor
MediaWiki+FCKeditor was a branch of FCKeditor developed for WYSIWYG wiki editing. Support for both have been discontinued.
Name change
The FCK in FCKeditor stands for Frederico Caldeira Knabben, the creator of the editor and the project's Benevolent Dictator for Life. Those letters resemble a well-known vulgarity in the English language (something that Frederico, a native Brazilian, was unaware of when he first released the program). As a result, Knabben changed the program's name to CKEditor beginning with v3.0. The CK letters now stand for Content and Knowledge.
Vulnerabilities
FCKEditor 2.5.1 and 2.6.6 contain a file renaming bug that allows remote code execution. Specifically, it is possible to upload ASP code via the ASP.NET connector in FCKEditor. The vulnerability requires that the remote server be running IIS. The vulnerability was discovered by security researchers from Rapid7 in August 2010.