The .NET Framework is a development and execution environment that allows developers to develop Windows Applications as well as Web Applications.
A program that is written to run under Microsoft Windows operating system is called a Windows applications(such as applications developed under VB.NET).
Web applications generally refer to programs that run on the Web server.(such as applications developed under ASP.NET with C# or VB)
The .NET Framework provides common platform to develop all types of applications( Windows, Web) by using a common set of tools, and also enables easy integration of modules.
Interoperability: .NET Framework supports communication b/w new and existing applications; therefore functionalities of the existing programs can be easily utilized.
Cross-Platform Support: Any .NET compatible language such as VB.NET/C# will be compiled by its own compiler and MSIL code is created. Further this, code will be compiled into native code with the help of Just-in-Time compiler and then application is executed.
Language Independence: Provides multiple language support by using the feature known as Common Type System(CTS) that is the component of CLR. So, with this feature we can build .NET applications in a number of languages such as C++, C#, Visual Basic.
Base Class Library: This Library provides a huge set of the Framework Class Library(FCL) for common tasks.FCL contains several classes for developing various applications such as: ASP.NET/VB.NET based applications.
Easy Deployment: .NET Framework makes the deployment process easier. Applications are deployed in the form of assemblies in .NET. Therefore ,registry entries are not required to store information about components and applications. Also assemblies store information about different versions also, and version problem is not there.