Linux runs the computing world. It is by far the most used operating system on servers and perhaps the only OS on supercomputers. It has taken over much of the mobile world thanks to Android and is on the cusp of taking a majority share in education via Chrome OS.
The one area where it has had difficulty expanding year after year is the desktop. Not because it's terrible at it but because it needs a few missing pieces that will stop the Year of the Linux desktop from being a running joke.