• The term 'web server' can be used to refer to either a computer program that uses hypertext transfer protocol (HTTP) to deliver web content over the Internet's world wide web, or a computer that serves this purpose by primarily running such a software. Content is viewable on other computers using a web browser; thus, whenever we visit a website, it is the web server that sends us the web pages we view.
  
  

Apache Web Server

• The Apache web server is the most popular, as well as the most commonly used, web server software in the world. It is open-source software and offers virtually unlimited modification possibilities. Apache is also free software and supports a vast range of free web technologies including PHP, Perl, Python, Ruby and many proprietary technologies. It is available for almost all major operating systems and hardware platforms including Microsoft Windows, Linux, BSD and other UNIX-based systems and OS/X. Apache offers community-based free support on the web, on forums and in chat rooms. Many service providers also offer support, for a fee.
  
  

Internet Information Services

• The second most used server on the Internet is Microsoft's Internet Information Services (IIS). This is the primary server used in deployment of Microsoft technologies such as 'asp.net' while supporting various other web technologies offered by third parties. It only runs on Microsoft server operating systems however, and is proprietary software, requiring licensing. This is justified by the support provided by Microsoft within the licensing agreement, as the Web Developers Notes states.
  
  

Apache Tomcat Server

• The Apache Tomcat web server is often used with Apache to run Java servlets and JSP code. It can be run along with other web servers, or even as a standalone web server itself when the only content to be served is based on Java servlets and/or JSP. A part of the Apache Jakarta Project that develops open-source and free software for the Sun Java platform, it also supports most of the operating systems supported by the Apache web server.
  
  

Sun Java System Web Server

• This free but closed-source proprietary web server is developed by Sun Microsystems. Despite its name, it does support non-Java web technologies such as PHP, Perl, Python, Ruby and ASP along with Java-based web technologies including Java servlets and JSP. Windows, Unix and Linux are also supported.