Microsoft IIS Express

ASP.NET sites and applications today are built using either the ASP.NET Development Server that comes with Visual Studio or with the IIS Web Server that comes with Windows.

With the ASP.NET Development Server you do not get the IIS features like SSL And URL rewrite. While with IIS Server you need administrator account and other security privileges. IIS Express is aimed to provide you with the full feature set of both the worlds so that we can develop and test web application with ease and simulate the real scenario easily.

IIS Express will work with VS 2010 and Visual Web Developer 2010 Express. It will run on Windows XP and higher systems and will not require an administrator account.

Reference: http://weblogs.asp.net/scottgu/archive/2010/06/28/introducing-iis-express.aspx