You can extend Google Sites with Google Apps Script. Google products look very simple and basic but because the Google team is giving us the ability to add Google Apps Script to Google Docs and Google Sites; the power becomes truly amazing.
We are working on several projects. What we want to do is to provide useful applications for the web. Our goal is to create our scripts so that they can be used by any number of organizations. After a script is purchased we share the specially designed Google document(s) that provide the configurations needed to make your application work and to safely store your data. We also provide a link which gives you the Web Application user interface.
The link provides a flexible user interface