Apple's released a number of different developer preview builds of OS X Mountain Lion in preparation for its release, and things took a huge step forward today: according to 9to5Mac, Apple has pushed the first Golden Master build out to developers. This doesn't mean the retail release is necessarily imminent, however; developers will still be looking to see if there are any show-stopping bugs, and Apple hasn't been shy about releasing multiple Golden Master builds before. Still, it's a sign that things are on track for the operating system to make its official debut later this month for $19.99.
Update: 9to5Mac is now also reporting that Apple has begun asking developers to submit their Mountain Lion apps for review so they can be ready in time for the new operating system's launch. Developers are also said to be able to submit iOS apps that take advantage of the new cross-platform GameCenter functionality that will allow Mountain Lion and iOS apps to work together.