With macOS Cataline some nice new safe feature appeared. Apple always try to defend users from malicious softwares. Unfortunately this can cause several "safe" apps and tools won't work any more.
If the message appears "\
In general you should delete these kinds of apps. On the other side if you know the app is safe you can get rid of this problem.
Find the app in finder, right-click on that and press 'Open' in the context menu. If this doesn't solve the problem go to 'System Preferences/Security & Privacy/General'. In the section 'Allow apps downloaded from:' the app should appear where you can give an exception to run it.
When the app doesn't appear you need more trick.
The problem comes from that macOS now places special 'quarantine' attributes to the downloaded content. You have to remove that.
If you have administrator rights on your machine open a terminal, and run:
sudo -rd com.apple.quarantine <full /path/to/your/app or file>
This command removes that annoying attribute.
Have fun! 🙂