By default osx doesn't allow opening unsigned applications.
This can be worked around by either
- changing the security preferences, or
- right clicking on the program, select open and click open on the dialog that pops up
The dialog that opens up if a users just dubble clicks the application looks like this:
To sign it you must enroll to the mac development program which costs $99 annually (which might be a bit much since not that many osx users uses the application at the moment)