OS X 10.9 Mavericks Developer Preview 5 comes a little over two weeks after the fourth preview was made available at the end of July. Due to an eight-day downtime after Apple's Developer Center was affected by an intruder, the timing of the latest Mavericks release is slightly off from the two-week cycle Apple had kept until Developer Preview 4.
Notable in the latest preview is the inclusion of iBooks for OS X, which was announced at this year's Worldwide Developers Conference in June. Like Apple Maps, iBooks will make the crossover from iOS to OS X when Mavericks launches this fall.
As with previous version of Mavericks, Dev Preview 5 contains minor backend changes. Release notes from a previous Developer Preview suggested changes were made to bring support for iCloud Keychain.
Apple's maintenance update for the current OS X 10.8.5 Mountain Lion, dubbed build 12F33, comes with no known issues and once again requests developers focus on graphics, Wi-Fi and wake from sleep functionality. Prior to the temporary Dev Center shutdown, Apple was releasing builds of 10.8.5 on a weekly basis.
Both Mavericks and the Mountain Lion update are slated to launch this fall.