NetLogo OS X 10.8 and later Compatibility Info
Depending on your system settings, installation of NetLogo may be blocked by Apple's "Gatekeeper" feature.
NetLogo versions before 5.0.4
If you try to install older NetLogo versions on OS X 10.8 or later, when you try to open the disk image you'll get a rather alarming-seeming dialog that says NetLogo is "damaged and can't be opened. You should move it to the trash." The OS is wrong; the application is fine. In order to open the disk image, you just need to open System Preferences, go to the Security & Privacy panel, and change the "Allow applications downloaded from:" setting for Gatekeeper to "Anywhere".
NetLogo versions since 5.0.4
Versions of NetLogo 5.0.4 and later will still be blocked if your Gatekeeper is set to "Mac Store App" only, but instead of Gatekeeper telling you that the file is damaged, it will tell you that it was not downloaded from the app store. Setting your Gatekeeper to "Mac App Store and identified developers" will permit installation.
The first time you open NetLogo, you will see a dialog informing you that "NetLogo is an application downloaded from the Internet. Are you sure you want to open it?" Clicking "Open" will dismiss the dialog and prevent it from showing when launching NetLogo in the future.
Note that NetLogo should be installed and launched for the first time by the same account (one with administrator privileges). Gatekeeper appears to prevent non-administrator users from opening applications downloaded from the internet.
For more details, see this Apple support document.