Justinmind allows you to try out your web apps and your mobile apps on your desktop computer. It allows you to view your web app numerous screen types and screen sizes. The Justinmind tool is very user friendly. It has a drag-and-drop system, which means there is no code involved in the prototyping process. You are able to use their preloaded UI kits, or you may start with a template and customize it yourself. It is a very visual and polished tool that even novice programmers will feel comfortable with.