Editors

• CodeMirror - http://codemirror.net/

"Stable, long history, used by Google (playgrounds). Supports a lot of languages, supports search & replace. Released under a MIT-style license"

• Ace - http://ace.ajax.org

"Used in Cloud9 IDE, supports many languages. Mozilla's Bespin/ Skywriter was merged into Ace, developed by Mozilla, Ace.org. Released under the Mozilla tri-license (MPL/GPL/LGPL)"

Transport layers

• Socket.IO

"Provides layer over ajax/ Websockets/ flashsockets for simple client-server message transmission."

Javascript/ design

• jQuery - http://jquery.com/
• Twitter bootstrap - http://twitter.github.com/bootstrap/