Which of the following are open-source vulnerability scanners?

Nessus was originally developed and released as open-source software by Renaud Deraison, establishing it as a recognized open-source vulnerability scanner before Tenable later transitioned it to a commercial model.

NetRecon was a commercial network vulnerability scanner developed and sold by Symantec, not an open-source product.

Hackbot is an open-source automated security scanning and vulnerability assessment tool freely available for security research and testing.

Nikto is a widely used open-source web server vulnerability scanner maintained at cirt.net that checks for dangerous files, outdated server software, and misconfigurations.