There are numerous web server applications available for Linux. The most popular is Apache. Others include nginx, Lighttpd, Cherokee HTTP Server, Jigsaw, Xitami, Zeus, Hiawatha, Caudium, Adobe JRun, Monkey HTTP daemon, TUX web server, and bozohttpd.
The Apache web server.
The apache http server
If you are running a Linux web server there is LVS. LVS is an open-source load balancer.
Apache is the world's leading and most commonly deployed web server. The majority of the web sites on the Internet run on an Apache server,
Apache Web Server is the most popular web server software on the internet. It is available for all major operating systems, and supports most application frameworks (except for .ASP).
all inside a computer is software, maybe you want know about software used in web services, like apache, this software help to up a web server.
This is software which is stored completely on a Web server.
The difference is simply what operating system the web host's servers are running. Linux web hosts typically support PHP, MySQL, and related software. Windows hosts typically support ASP and related software (along with some form of an SQL server, but that varies by host). It does not matter whether you run Windows or Linux (or another operating system) on your machine.
Facebook uses open source software, including the Linux operating system, Apache web server, and MySQL database. Many other large online sites use open source software; for example, Google and Wikipedia use Linux servers.
Probably Apache
You need to install a web server, a database server, and PHP to support the drupal software. It is common to use the Apache web server and the MySQL database server. Installers are available to install all these at one time. Instructions are available at: http://drupal.org/node/263 .
If you are inquiring about the software that actually runs the web server, there are many solutions available. Apache is the most popular web server in the world. It is designed to provide a large number of features and scale across large and powerful servers, though it can even be run on a reasonable home desktop. Apache is available for Windows, Mac OS X, Linux, and FreeBSD. Lightppd is a fast and lightweight web server. Many sites, such as Wikipedia and YouTube, use it to serve files to users. It supports most of the features of Apache, but consumes less than half as much RAM. Lighttpd is available for Windows, mac OS X, Linux, and FreeBSD. IIS is a web server designed and developed by Microsoft, and is the second-most popular web server on the internet in terms of usage. It is designed to integrate with proprietary Windows features like ASP and .NET. IIS is only available for Windows 2000, Windows XP Professional, Windows Server 2003, Windows Vista, and Windows Server 2008. It is not included with XP Home, but can be installed through an unofficial workaround.