Two things, since the binary is missing the executable permission and the app is not signed:
- You'll need to add make the main executable, uh, executable, following these steps (knowledge of the command line is needed):
- Open Terminal
- Navigate to "floppy minecraft mac.app/Contents/MacOS"
- chmod +x not\ minecraft\ dont\ sue\ me\ pls
- You'll need to go to System Preferences -> Security & Privacy and allow it to run.