That's not the only reason of trouble on Mac OS X Mavericks.
Even after enabling downloads from any source it still don't work.
kittehcoin-qt cannot be opened because of a problem
I have received the reports of Mac Wallet issues, I am looking into these now and will have a fix posted ASAP. It seems the new Mac Wallet works for most people but not all, some people are getting "Application cannot be opened because it is from an unidentified developer" error. Fixing.
Yes that is because they have the security feature turned on for apps. If you experience this: open system preferences and click "Security & Privacy" at the bottom of that window there should be information about the app trying to run. click open anyway (or whatever the text is) and you will run the app. alternatively you can change the "Allow apps downloaded from:" -setting to anywhere, double-click the app and then reset it to whatever security setting you had before.
should work