Loki will transform any textarea entry field into a "what you see is what you get" (WYSIWYG) editor.

Loki is different from other opensource browser-based WYSIWYG editors in its focus on web standards compliance and in its encouragement of semantic markup.

Introduce the designMode property & the like

uEditor is a WYSIWYG HTML editor originally based on widgEditor designed by Cameron Adams, but rewritten for jQuery and considerably modified since.

markItUp! is a JavaScript plugin built on the jQuery library. It allows you to turn any textarea into a markup editor. Html, Textile, Wiki Syntax, Markdown, BBcode or even your own Markup system can be easily implemented.