OpenVAS, which we just looked at, is a general-purpose vulnerability scanner. It can find vulnerabilities for any kind of operating system or for any server daemon. However, as we've just seen, an OpenVAS scan can take a while to run, and it might be more than what you need.
Nikto is a special-purpose tool with only one purpose; that is, it's meant to scan web servers, and only web servers. It's easy to install, easy to use, and capable of doing a comprehensive scan of a web server fairly quickly. And although it's included in Kali Linux, you don't need Kali Linux to run it.
