Microsoft's new Fluent Design System
From the looks of it, Microsoft is experimenting with the design of a new email client, file system, and desktop, among other things.
Microsoft has long made interesting proofs of concept, but has been inconsistent on execution. I wonder how far they'll see this through.
It's hard not to see this, as well as Google's material design, as both a response to and an attempt to differentiate from Apple on design. Apple has helped make design into popular art, but concepts like these (including Apple's own iOS 7 introduction video) feel like attempts to justify a visual style by associating it with better usability, instead of starting with usability and allowing that inform the look and feel.
For example, translucency can look great but I don't think it does much for usability. Yet we hear rationales for it using terms like depth and context. What usability really needs is contrast: definition between objects, clearly delineated buttons, and visible UI that is not hidden behind gestures or collapsing application frames.
In many ways, so-called "flat" design has moved us away from usability in pursuit of aesthetics. Microsoft seems late to arrive at this style as I'm starting to feel the pendulum moving back towards more substantive, usable design.