ASP.NET is a set of Web development tools offered by Microsoft. Programs like Visual Studio .NET and Visual Web Developer allow Web developers to create dynamic websites using a visual interface. Of course, programmers can write their own code and scripts and incorporate it into ASP.NET websites as well. Though it plays a major role as a successor to Microsoft's ASP programming technology, ASP.NET also supports Visual Basic.NET, JScript .NET and open-source languages like Python and Perl.
If you want to try ASP.NET, you can install Visual Web Developer Express using the Microsoft Web Platform Installer, which is a free tool that makes it simple to download, install, and service components of the Microsoft Web Platform. These components include Visual Web Developer Express, Internet Information Services (IIS), SQL Server Express, and the .NET Framework. All of these are tools that you use to create ASP.NET Web applications. You can also use the Microsoft Web Platform Installer to install open-source ASP.NET and PHP Web applications.