With the many updates and new features announced for the upcoming OS X release of Mountain Lion, one may have slipped by, but it's an important feature. It's also likely to become controversial.
Gatekeeper gives users some extra security when running third party software. Apple says Gatekeeper will help prevent users from "unknowingly downloading and installing malicious software." The system preference has three levels of security. One only allows you to install apps from the Mac App Store. A second level allows installation of apps from what Apple calls "identified developers." Apple is starting up a program that basically allows developers to have digital signing of their apps. The lowest level of security allows apps to be installed from any source, but OS X will warn you if the app is not digitally signed.
What Gatekeeper doesn't do is protect you against malware and viruses, which admittedly have not been a big problem on the Mac platform. Apple does have some built in tools to identify potentially harmful programs, but sometimes the problems can get ahead of Apple implementing a solution. Of course, Windows faces similar challenges, but on a much larger scale.
Gatekeeper is in the recently released developer preview, but it is not activated. AppleInsider reports that it can be turned on by using the new OS X system policy control command-line tool "spctl(8)".
It will be interesting to see if Gatekeeper matures and adds features by the time Mountain Lion is released in late summer. We'll do a deeper dive on Gatekeeper and its possible implications for the Mac platform later on.