Apache HTTP Server – The most widely used of them all, Apache is a free and open source web server that is available through most Linux distribution repositories.

Microsoft IIS – IIS comes standard with Windows Server 2008 and previous server versions. Although other web servers will run on Windows, IIS is the primary one. It is distributed on a commercial license.

Sun Java Web Server – Before its acquisition by Oracle, this was Sun’s primary web server technology used on Sun’s hardware appliances. It is, however, cross platform, and some of its source code is released under a BSD-style license.

Ngnix – Pronounced “Engine X”, this lightweight web server is a very popular alternative to Apache. It runs on Unix-like and Windows operating systems and is available under a BSD-style license. It is the fourth most popular web server, according to NetCraft.

Lighttpd – As the name implies, this web server is designed to be lightweight in its CPU and RAM usage but is actually heavyweight in its ability to withstand onslaughts of traffic. It does not have a lot of the modules offered by Apache and others, but it makes up for that in speed. Popular high traffic sites like Wikipedia and YouTube use it.