Internet services company Netcraft released its monthly web server survey yesterday, aptly titled June 2009 Web Server Survey.
The survey monitored some 238,027,855 sites over the last month. It tracked a wide variety of things, including server platform market share and the number of websites hosted by these servers, which increased dramatically.
More servers are running Apache than any other platform with other industry players like Sun and Microsoft making very little headway in catching up. One platform, nginx, did climb 1%, mainly because it is used by blog hosts like WordPress, which have seen an explosion in users recently.
Apache is so popular because it is free, open-source, and easy to customize for use in a variety of scenarios. Chances are very high your host is running it.