Nokia is once again extending and improving Windows Phone. While Microsoft has implemented Live Tiles across Windows Phone, Nokia is adding a new App Folder interface that allows Windows Phone users to stack apps and settings into a folder Tile on the Start Screen. The new feature is part of Nokia's Lumia Black software that is being rolled out to Lumia 1020 and and Lumia 925 devices today. Other Lumia models will be updated "in the coming weeks" according to Nokia.
I'm not sure what's more telling about the state of the Windows Phone platform; the fact that folders on the homescreen is a big thing, or that Nokia, and not Microsoft, implemented it.