CodeShare.io - Realtime code sharing for developers
WordPress - WordPress is web software you can use to create a beautiful website or blog. We like to say that WordPress is both free and priceless at the same time.
CodePen - A front end web development playground.
Liveweave - Liveweave is a HTML5, CSS3 & JavaScript playground for web designers and developers
Plunker - Plunker is an online community for creating, collaborating on and sharing your web development ideas.
Visual Studio Live Share - Real-time collaborative development