As was promised in today's WWDC keynote, Apple has released OS X Mountain Lion Developer Preview 4 today, a build which the company described as "near-final." 9to5Mac has posted the release notes, which indicate that the number of bugs is decreasing and Game Center is getting close to being in full working order. It's not yet known whether or not all of the new Mountain Lion features showcased today are included in this build, but Facebook integration at least can be enabled with a separate download. If they're not, they certainly ought to be in the next one: Apple has committed itself to a July launch of the new OS. Once released, Apple will charge $19.99 for either Lion and Snow Leopard users.