Jason Snell with more info on Gatekeeper and how it works.

It’s clear that Gatekeeper in Mountain Lion isn’t intended to be some sort of high-security app lockdown. It’s just a tool to encourage people not to run software they don’t trust. If they really, truly want to run an app, Mountain Lion won’t stop them.

Gatekeeper also strikes me as a way to continue to build support for the Mac App Store. Apple is telling users that 3rd-party apps bought from the Mac App Store apps are the most safe.

And, Apple is pushing support for the Mac App Store from the other direction as well. John Gruber points out that some of the best new features in Mountain Lion will only be available to Mac App Store apps:

Two big ones: iCloud document storage and Notification Center. Both of these are slated only for third-party apps from the Mac App Store. Many developers, though, have been maintaining non-Mac App Store versions of their apps. If this continues, such apps are going to lose feature parity between the App Store and non-App Store versions. Apple is not taking the Mac in iOS’s “all apps must come through the App Store” direction, but they’re certainly encouraging developers to go Mac App Store-only with iCloud features that are only available to Mac App Store apps (and, thus, which have gone through the App Store approval process).

February 16, 2012