Windows Webserver is described as 'The Windows Webserver was developed for testing PHP and CGI/FCGI programs under Windows, without installing an Apache or IIS environment. The Webserver is easy to install and comes with buildin PHP 8.0.8 FastCGI support, mod_rewrite and SSL/TLS 1.2' and is an app in the Development category. There are more than 50 alternatives to Windows Webserver for a variety of platforms, including Windows, Linux, Mac, Self-Hosted solutions and BSD. The best alternative is XAMPP, which is both free and Open Source. Other great apps like Windows Webserver are Apache HTTP Server (Free, Open Source), nginx (Free, Open Source), WampServer (Free, Open Source) and Caddy (Free Personal, Open Source).
Simple: It handles only the minimum necessary to implement HTTP/1.1. Well, maybe a little more than the minimum. Small: See the comparison chart. It also has a very small run-time size, since it does not fork and is very careful about memory allocation.