What should I do if i can't open the app
If it says that the program is damaged, its a safety thing by apple. By default, apple only lets you open programs with certificates, but I havent got one. So you should allow it to run any program. Or try downloading it on windows, and then open it on mac.
Other solution: I tested it with the unzip-tool "StuffIt Expander", and it works. (You find it in the App-store)