The Mac OS X 10.9 Mavericks will replace the OS X Mountain Lion which was unveiled in July last year and will be released to developers today and will be made public sometime in autumn. There were reports earlier that OS X team was pulled to work on iOS 7.
Some of the new features of the OS 10.9 include Tabs in the Finder, tagging, iBooks and Maps app, better battery life, iCloud keychain, quick reply for messages, lock screen notifications, auto updating apps, better multiple display support, compressed memory, redesigned calendar UI among others.
We earlier reported that signs at the Moscone West convention centre indicated the launch of next version of OS X along with iOS 7. OS X reports have come true and we will probably see the launch of iOS 7 as per the sign boards and as claimed by WSJ through a new report.