IIS is Microsofts implementation of a web server for Windows. It’s free to use with Windows Server and can even be deployed on a Windows 10 machine. IIS is an easy to use GUI and may be preferred over Apache or NGINX when building web apps that fully utilize the Microsoft Stack.
Apache is the go to web server for deploying websites. You can run it on Linux, Windows, Mac, Unix and more. It’s free, and reliable.