It enables an unprecedented level of software integration through the use of XML Web services: small, discrete, building-block applications that connect to each other—as well as to other, larger applications—via the Internet.
What does this really mean?
Microsoft .Net (Microsoft dotNet) aims to reduce the cost of software development by creating re-useable code that can be used by all applications in the environment, regardless of operating system or programming language. You may develop (or purchase) a Microsoft .Net (Microsoft dotNet) web based application that takes new sales orders over the Internet.
Dot net will allow you to call the logic behind the application from any other program. For example Microsoft Excel or Word macros could directly call the web based application to create new sales order. A customer could easily and securely develop their own application interface that directly and securely places a new sales order on your website.