Apple today released the fourth beta version of OS X Mavericks 10.9.5 for developers. Compilation 13F18 brings basically the same focus areas as the third (Safari, USB, USB Smart Cards and graphics, and Thunderbolt), in addition to also asking developers to test the Gatekeeper feature. The update is available through the built-in OS X update system (on the Mac App Store) or through the Apple developer portal.
Update, by Rafael Fischmann · 08/20/2014 s 19:51
A day later, Apple also made available to developers the Safari 7.1 beta 3 (for OS X Mavericks) and the Safari 6.2 beta 3 (for OS X Mountain Lion). Release notes can be found in this PDF of the Mac Dev Center.
Update II, by Rafael Fischmann · 08/20/2014 s 21:46
And the OS X Server 3.2 Developer Preview, from build 13S5165.