Alongisde the iOS 6 beta, Apple has also seeded OS X Mountain Lion Developer Preview 4, making it available in its Dev Center. This is a near-final version of Mountain Lion, and as such, there aren't many areas of concern listed in the seed note. It makes sense, since Mountain Lion will be released next month. If you're a Mac developer, you can grab build 12A239 now, as promised in the WWDC 2012 keynote.