Craig Federighi took the stage after Tim Cook offered some updates on apps and iOS 7 and said the Apple software team wanted to give users a hardware upgrade through software. As such, Mavericks promises to increase battery life and compress inactive parts of memory (so you can run more applications without slow down). It also adds Open CL for integrated graphics, and a host of other new features including shared links, enhanced notifications, iBooks, notifications, a new improved Calendar app, and more.
The biggest piece of news about Mavericks is that it's free for some Macs going back to as far as 2007. Whether you're going from Snow Leopard or Mountain Lion, you can update to Mountain Lion for free starting today.
Stay tuned for more on Mavericks!