The "App River" is a table of 120 interlinked iPads here on the second floor of the Moscone Center at WWDC2012. The "river" is a flow of apps moving along at a constant but relatively slow pace down a channel 4 iPads wide, from one end to the other about 30 iPads long. Each individual iPad contains 108 icons, making the whole river about 12,000+ apps icons visible at an overall glance. The apps are organized by hue, and each app icon flashes white when a download is registered. The total length of the river (including offscreen apps) is the top 20,000 apps on the app store.
You can interact with the flow in two ways. Running your finger across the face of the iPads will cause a ripple effect to emanate across the proximate icons giving a fluid-like disturbance effect. You can also tap individual icons to display an information pop-up that shows a graphical download indicator as well as the name and some other minor bits of info about the app.
This installation is probably worth at least $60,000 @ $500 per iPad.