There are a superfluity of tools and utilities on the internet that you can utilize to rapidly develop your web application. Whether you want to deploy your own personal home page or a website for your organization or simply any web app, these tools not only assist you to quickly learn the tricks of the trade, but also help in rapid and powerful client side code development.
Before such tools came into existence, you probably had no other option but to use some third party tools such as Flash in order create even a straightforward animation for your web app. MooTools gives you the power to create optimized effects and transitions with the use of predefined functions available in its library. However if your animation requirements are very high and involve complex tweening, transitions and effects, you would probably stick to using a third party application altogether.
As mentioned earlier, a plethora of similar and powerful tools are available alongside MooTools such as scriptaculous, jQuery and so on. It just depends on your ability to adapt to a particular syntax, which should enable you to decide upon a tool you would be using, and start developing your web app right away!