Karlson does not properly work on macOS without some intervention. Karlson is not set as an executable, so it will not open and you'll receive the error "Karlson cannot be opened." On top of this, Dani is an unidentified developer, which means that it cannot be opened by default. This can be fixed easily:
1. Make sure Karlson is in the Applications folder
2. Open the Launchpad and open Terminal
3. Type "cd /Applications/Karlson_mac.app/Contents/MacOS"
4. Type "chmod +x Karlson"
5. Type "sudo spctl --master-disable"
6. Enter your password
And that's all, Karlson should now open properly.