When Microsoft set out to build the next-gen Windows Explorer for Windows 8, it did so with three goals in mind: optimization for file management tasks, streamlining the command experience and ensuring that the heritage of this core OS component survives through an evolutionary leap.

Alex Simons, from the Windows Program Management team, is featured in a video shared by the Redmond company, explaining the evolution of Windows Explorer.

Long story short, Windows 8 Explorer sports a brand new graphical user interface, which the software giant is referring to as the Ribbon UI or the Fluent UI.
8 Reasons Windows 8 Explorer Ribbon UI Is Better than Its Predecessors - Softpedia