Pronounced “dot-net”, .NET is a proprietary Microsoft platform designed for developing web applications. Although it is not free, Microsoft offers a large library of components that you can mix and match to build your site’s functionality. Unlike most open-source modules, the advantage of using .NET is that the library of functions comes with full technical support. A major difference between PHP and .NET code is that .NET code must be compiled into a web application that lives on the server.
Compiled code is believed to be safer because no one can see the source code embedded in the HTML as you can with PHP. Like PHP, there are a lot of developers who are familiar with .NET.