Multitouch gestures.
So, now, Lion can count on multitouch.
From the beginning, you can have beautiful, fluid, momentum-based scrolling.
You can have incredible multitouch taps to zoom in on stories or pictures.
You can dynamically zoom with beautiful, fluid pinch motions.
You can swipe through your photographs or slides, your webpages, all with an incredible physical realism that's never been possible with a PC operating system before.
Here's a simple example, the scroll bar.
Why do we have scroll bars?
Scroll bars are there so you could click with the mouse and drag and scroll, but now if you're pushing your window with multitouch, you don't need them.
They can disappear.
You're gonna have a much more beautiful reading environment, but when you go to scroll, they magically appear, give you a sense of place in proportional size, and then disappear when you don't need them.
So multitouch is now built throughout the system in a very powerful way.