While we still await the release of iOS 7 beta 4, Apple has gone ahead and seeded the fourth developer preview of OS X Mavericks for beta testing today. The release comes two weeks after the third developer preview was made available, and the build is available to anyone that already has one of the previous versions of OS X Mavericks installed on their machine.
OS X Mavericks will be released to the public this fall on the Mac App Store, and is largely considered to be an iterative update over Mountain Lion. The new software caters heavily to power users, with new features such as Finder tabs, file tagging and improved support for multiple displays. iBooks and Maps also make their debut on Mac, alongside improved versions of Calendar and Safari.