Apache runs more than 60 percent of all websites. Its share of high volume web sites is even greater. This is the software that forms the web pages and sends them to your browser. It involves the execution of server side application code like python, perl, php or Java. It involves looking up or updating data in backend databases like Postgresql or MySQL. These functions are implemented in modules that can be “mixed and matched” to create customized configurations.
Apache runs on many different software platforms, various Linuxs running on different hardware, Windows, Mac and various older Unix variants. This software is called middleware. It is there working behind the scenes gluing many different system elements together. It does not get the credit it deserves. Apache is the printing press of the Internet revolution.