CodeShare.io - Realtime code sharing for developers
CodeKit - CodeKit allows you to optimize the performance of your website by automatically and efficiently compiling a variety of popular languages.
CodePen - A front end web development playground.
Ghostlab - Ghostlab allows you to test out a newly developed website on a variety of browsers and mobile devices at the same time. To get started, simply drag the web address to the Ghostlab system and press the play button. Read more about Ghostlab.
Liveweave - Liveweave is a HTML5, CSS3 & JavaScript playground for web designers and developers
Browsersync - Browsersync makes your tweaking and testing faster by synchronising file changes and interactions...