Apple has sent an email to developers prompting them to submit their applications for OS X Mountain Lion.

Make sure your apps take advantage of the great new features in OS X Mountain Lion
when the world’s most advanced operating system ships to millions of customers
worldwide. Download OS X Mountain Lion GM seed and Xcode 4.4 GM seed, now
available on the Mac Dev Center. Build your apps with these latest seeds, then
test and submit for review.

You can also submit iOS apps that take advantage of the new cross-platform Game
Center Groups, so they’ll be available when OS X Mountain Lion ships.