OS X 10.9 Mavericks Developer Preview 5 comes a little over two weeks after the fourth preview, a later than usual delay after Apple's Developer Center was affected with some serious downtime after a hacking attack.
The biggest inclusion in this iteration is iBooks, the first time the popular iOS reading and book sales app has made its way across to laptops and desktops. Apple Maps is similarly set to make the transition across.
The operating system is so far only available for approved developers.
Apple also today released a maintenance update for OS X 10.8.5 Mountain Lion, known as build 12F33, which requests developers focus on graphics, Wi-Fi and wake from sleep functionality.
Mavericks is scheduled for release in Spring this year.