Linux range of use
Linux kernel-based operating systems have found wide adoption and a very far-reaching range of use.
Linux on the desktop
The common human interface devices (HIDs) available for desktop computers, laptops and similar devices determine the design of the (graphical) human-computer interface implemented into software. There are a couple of software packages to chose among, when building an accordingly designed graphical user interface.
Linux as gaming platform
As the adoption proves, the Linux kernel is suitable as kernel for a gaming platform. Of course additional software is necessary to either augment a typical desktop installation to be suitable as a gaming platform or to create a Linux operating system for the sole purpose of being a gaming platform.
Linux for server
There is an abundance of server software that runs on top of the Linux kernel.
And there are a couple of widely known Linux-based solution stacks, e.g. the LAMP (software bundle).
Linux for mobile devices
One of the best known Linux bases operating system for mobile devices, such as smartphones is the Android (operating system). Android employs a modified Linux kernel and combines this with libbionic instead of the glibc, SurfaceFlinger as display server, and some other replacements specifically written for this purpose.
Many mobile devices have a touchscreen as their sole human interface device (HID). The GUI and partly the middleware of the operating system has to be adapted as to enable software designers to create an according human-computer interface.
Linux for embedded systems
Also because there are patches maintained that transform the Linux kernel into a Real time kernel, it has found very wide adoption as kernel for operating systems driving embedded systems. An non-RTOS example which is at the same time a Linux distribution is OpenWrt.
Linux for supercomputers
480 (96%) of the worlds fastest supercomputers run some Linux operating system.