CodePen - A front end web development playground.
Charles Proxy - HTTP proxy / HTTP monitor / Reverse Proxy
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
JS Bin - Sample of the bin:
Postman - The Collaboration Platform for API Development