CodePen - A front end web development playground.
Pretzel - Keyboard shortcuts for the app you're currently using
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
KeyCue - Menu shortcuts are supposed to provide quick access to frequently used menu commands.
Liveweave - Liveweave is a HTML5, CSS3 & JavaScript playground for web designers and developers
Hotkey Commander - Find out and override what hotkey combination is registered by which application.