OS X Mavericks will be a free download
Apple has just announced the latest version of OS X, 10.9 Mavericks, will be available as a free download. In addition to the usual promise of increased speed and efficiency, the update has a number of improvements over 10.8 Mountain Lion, including a more robust notification system (which includes inline replies), better support for multiple monitors and full screen apps, a revamp of Finder, and the addition of iCloud Keychain for saving passwords.
Many other apps have been updated, but although some are getting a boost in functionality, a lot of the work done brings the overall aesthetic of OS X in line with Apple's iOS 7. Gone are the Contacts app's fake book and pages, gone are Calendar's torn page marks, and gone is the Notes apps' yellow legal pad.