CodePen - A front end web development playground.
Thunkable - Powerful but easy to use, drag-and-drop mobile app builder.
JSFiddle - Test your JavaScript, CSS, HTML or CoffeeScript online with JSFiddle code editor.
MIT App Inventor - App Inventor is a cloud-based tool, which means you can create apps for phones or tablets right in your web browser.
JS Bin - Sample of the bin:
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.