If you’ve gotten OmmWriter from our downloads page and recently also upgraded to Mountain Lion, you may get a message saying that OmmWriter cannot be run because it’s an app from what Apple calls an unverified developer.
This is related to a security feature in Mountain Lion called GateKeeper. Apple is slowly changing to a model where all apps are signed by them, and only signed apps are allowed to run. If you’ve gotten OmmWriter from our downloads page, and not through the App Store, it will not be signed, and therefore produce the error message. All versions of OmmWriter are still the same and safe to use on your Mac.
You can fix the issue by going to System Preferences on your Mac and set GateKeeper to allow your computer to run apps from any developer.
The below article from Apple explains in detail:
Ivin and The OmmWriter Crew