Microsoft Visual Studio 2008 Professional [patched] -

VS2008 was built on WPF (Windows Presentation Foundation) long before WPF was cool. The IDE itself was a guinea pig for its own technology. You could feel it: the slight lag when dragging tool windows, the cinematic fade of the start page, the fact that you could use XAML to actually design a UI that didn't look like a spreadsheet from 1995. It was buggy. It was heavy. It was glorious.

Integrated support for ASP.NET AJAX and a "Split-View" HTML editor for simultaneous code and design views. Microsoft Visual Studio 2008 Professional