For students and hobbyists, Tenable offers . While this uses a different type of key, it’s worth noting that it limits you to scanning 16 IP addresses. It is a great way to learn the interface without the "Professional" price tag. Activation and Installation
It transitions the software from a non-functional state to a fully operational scanner. nessus professional license key
If you are decomissioning a machine, you should "unregister" the scanner in the settings to free up the key. For students and hobbyists, Tenable offers