Most web developers have a particular development environment on their computer. They may have the .NET Framework version 3.5 and Visual Studio 2008 installed, along with Microsoft SQL Server 2005, Internet Explorer 7 and Firefox 3. In a perfect world this environment would be static and the developer would not need to install beta or old versions of software that may or may not allow side-by-side installation with the current version. But in the real world, the site needs to be tested against Internet Explorer 5.5, 6, and the beta version of version 8, as well as against Firefox 2. And the developer may want to install the the ASP.NET Futures, which provide an early preview of future functionality for ASP.NET.