Yesterday, Apple seeded its new beta for OSX 10.5.7 to the developers. This is the 7th major update (as compared to 11 in Tiger) and it seems that Apple is planning to make Leopard a bit more stable before releasing the new Snow Leopard. The build number for this beta of Leopard is 9J22. In the current form it is a 440 MB file.
Apple has requested that developers test twenty areas of this particular build. People familiar with build number 9J22 say it has about 70 changes, mostly based on syncing issues related to Mail, Address Book etc. and networking improvements. Quite a few preferences and widgets have been updated as well to boost the performance. A big issue that seems to have been solved is the rejection of a few file types by Safari. This build also improves the way OS X handles the RAW image files.
A negative part of this update is that you can't use the new Safari 4 Beta. Other updates involve graphics drivers, Time Machine, printing services, screen sharing services, MobileMe syncing, AirPort services, text services, and iCal.
These betas are available for download and testing by Apple Developer Center Premier and Select Members.