A web server software is a program that does the receiving and answering of page requests using the HTTP protocol. This content is frequently in the form of HTML documents, images, and other web resources, but can include any type of file. The content served by the web server can be pre-existing (static content) or generated on the fly (dynamic content).
Below are the latest statistics of the market share of the top 3 web servers on the Internet by Netcraft Survey:
Top 1: Apache
The Apache HTTP Server Project is an effort to develop and maintain an open-source HTTP server for modern operating systems including UNIX and Windows NT. The goal of this project is to provide a secure, efficient and extensible server that provides HTTP services in sync with the current HTTP standards. Apache httpd was launched in 1995, has been the most popular web server on the Internet since April 1996.
Top 2: Microsoft IIS
Internet Information Services (IIS) for Windows Server is a flexible, secure and manageable Web server for hosting anything on the Web. From media streaming to web applications, IIS's scalable and open architecture is ready to handle the most demanding tasks.
Top 3: nginx
nginx is an HTTP and reverse proxy server, as well as a mail proxy server, written by Igor Sysoev. For a long time, it has been running on many heavily loaded Russian sites including Yandex, Mail.Ru, VK, and Rambler.