[wtallis]

None of Apple's platforms became a walled garden. iOS is more open than it was at first release when there was no SDK and the only sanctioned development method was web apps. OS X/macOS has acquired an optional walled garden app store but has otherwise only become more restricted for security reasons, and those restrictions can be disabled by the user.

None of the predictions of doom have come to pass. Users have come to accept new mobile computing platforms that are less open than the PC platform, but there is no "whole ecosystem" that has transitioned to being a walled garden.

[glogla]

Wait, doesn't the newest version of OS X remove the option to install applications that aren't from App Store or Certified developers?

You can still enable the option through console, but the UI option is gone.

[eridius]

I didn't realize it, but you're right, they removed the UI option. And that's probably a good idea, because anybody who isn't capable of turning that on with the Terminal probably shouldn't. It's a good bit of security. And you don't even need to change that option to run non-signed apps anyway, since you can always right-click the app and select Open and it will allow you (after a warning) to launch it anyway even though it is unsigned (and IIRC it only warns you for quarantined apps, so once you've launched it this way you can launch it normally afterwards).