There are two categories of apps:
- Metro style apps
- Desktop apps
Desktop apps are what we're all familiar with now in Windows 7 and past versions of Windows. Metro-style apps are touch-enabled and have fluid interfaces that mimic Windows Phone 7.
As for the technologies that these apps can be built with, this image from the conference sums it up pretty well...
Some Silverlight developers were worried that the App Store would only support HTML5, but clearly that's not the case. XAML has its place on Windows 8 as well.