Apple released the third beta of OS X 10.8.5 (build 12F17) to developers today. In the seed note Apple asks developers to focus on Wi-Fi, Graphics, Wake from Sleep, PDF viewing, and Mobile Device Management.
Given the planned release of OS X Mavericks this fall, 10.8.5 could very well end up being the last major version of Mountain Lion before Mavericks ships to the public. A developer beta of Mavericks was made available to developers the week of WWDC.
- Source Apple