Most operating systems, like Windows 10 or macOS, are designed to do multiple things. After all, many people want their computers to serve many tasks, such as productivity, media, and gaming. Some operating systems, however, are targeted at a single use to minimize the overhead and maximize the power of the hardware. Not to mention, it can create a more immersive experience.
One such focused OS is OpenELEC. This Linux distribution is designed to serve as a media center -- nothing more, nothing less. Today, the popular distro reaches stable version 7.0. There are images for both x86 and Raspberry Pi 2 and 3, meaning there is a very good chance you own compatible hardware.