So, this is the new Start screen for Windows 8. It's a brand new interface for tablets. It looks a lot like Windows Phone Live Tiles. And hey, that looks like an app store.
All apps can be viewed in this tile-based UI, which Josh from TIMN says is, "Very impressive. It looks super fast." You can totally see the Windows Phone influence on the interface, from the Live Tiles (which show info without having to open the app) to the touch keyboard, which even has a "thumbs" mode. (Sinofsky tells All Things D, "We were clearly influenced ourselves by phones.")
The animations and gestures and multitasking are all pretty damn smooth looking, as you can see in this demo video (or you know, up top). Swiping from the right reveals the taskbar, with the Start button, search, share and settings. Swiping from the left switches between apps, the background application zipping in and unfurling like a magic carpet. Snapping lets you have two apps next to each other, simultaneously. The main app takes up most of the screen, while the secondary app is like a docked sidebar; you can swap which you've got snapped very rapidly by swiping from the left to cycle through background applications.