Arguably
..99% of Apache servers run on Linux. But Linux runs also a lot of other things like Stock Exchanges, the Google Search Engine and Facebook.
So, arguably, Linux is the biggest Free Software Sucess Story. There is no need for the oversized, fatty and slow-moving american corporation to build and maintain the core infrastructure of the internet and the datacenter.
Individual skilled persons and small companies are sufficient to build largest-scale systems in the 21st century. Microsoft is on the intellectual decline, while all sorts of new concepts appear in Linux, BSD and many other places such as PHP, Ruby, LSM, Hadoop, JavaScript, Bittorrent and much more.