Unzip the application, move it to your Applications folder.
Then go to the Terminal app and run the two following commands:
chmod +x /Applications/Digital-Logic-Sim.app/Contents/MacOS/Digital-Logic-Sim
xattr -dr com.apple.quarantine /Applications/Digital-Logic-Sim.app
Now you can run Digital-Logic-Sim like normal, and it'll work fine until you upgrade your version when you'll need to do the same again.
Note that second command means MacOS will run the app, even tho it hasn't been validated by Apple. Do so at your own risk, and run the above commands at your own risk too... you probably shouldn't be running commands left by random internet people in Terminal.