How do I open a game or a demo that Gatekeeper recognises as being from an "unidentified developer"?

If you have Gatekeeper (a feature of OS X 10.7.5 Lion and later) installed, you may receive an error message when you try to open older applications from Feral, such as older games or demos, saying that the application "can't be opened because it is from an unidentified developer"

You will be able to download and install the application as normal, but to open it, you will need to do the following:

  1. Press the Control (ctrl) key and click on the application icon.

  2. Select Open from the pop-up menu.

  3. A dialogue box will appear, warning you that this demo is from an "unidentified developer". Click Open.