OS X 10.9 Mavericks Developer Preview 5 arrives just over two weeks after the fourth preview was released. Apple strayed from its two-week cycle on this occasion, due to the lengthy Developer Center downtime caused by an "intruder".
The new Mavericks preview gives developers a chance to test iBooks for OS X for the first time. The app was announced as part of the unveiling of Mavericks at WWDC in June, but hasn't been included in the preview until now. For a closer look at Mavericks' new features, see OS X Mavericks preview
The iPhoto update set to arrive with Mavericks also has a new beta version in the fifth preview. The 9.4.6 update brings a significant performance boost to iPhoto.
Alongside the new Mavericks preview, Apple has also seeded a new version of OS X Mountain Lion 10.8.5 to developers this week. The update is the eighth beta version of 10.8.5, and contains no known issues.
OS X Mavericks and the new Mountain Lion update are set to arrive in the Mac App Store this autumn. See: Mac OS X Mavericks release date
The new previews follow Tuesday's release of iOS 7 beta 5, which brings design tweaks, bug fixes and other improvements to Apple's upcoming mobile operating system for iPad, iPhone and iPod touch.
See: Apple iOS 7 preview