Amazon's Fire TV and Fire Tablet devices run a modified version of Android called Fire OS that allows you to stream music and video from Amazon, Netflix, and a wide range of other services. You can download and install third-party apps from the Amazon Appstore, and while Amazon doesn't publicize this fact, it's also possible to sideload third-party apps. But Amazon also does its best to restrict what you can do with its Fire OS devices and in recent years the company has cracked down even further by doing things like preventing users from sideloading some applications.