JS Bin is a webapp specifically designed to help JavaScript and CSS folk test snippets of code, within some context, and debug the code collaboratively. JS Bin allows you to edit and test JavaScript and HTML (reloading the URL also maintains the state of your code - new tabs doesn't). Once you're happy you can save, and send the URL to a peer for review or help. They can then make further changes saving anew if required.
The OpenLaszlo platform allows developers to create applications with the rich user interface capabilities of desktop client software and the instantaneous no-download Web deployment of HTML.