Steve Jobs has just announced the eighth iteration of OS X, dubbed Lion, complete with a monumental new feature, the Mac App Store. Other changes are still pouring in, such as improvements to syncing, full screen app displays, auto-updates, Mission Control (a combination of Spaces and Expose), gestures and more.
Read more about OS X Lion on Apple's site here.
Updates: Lion will be available summer 2011. The Mac App Store will be available in 90 days.