Fire OS is Amazon's customizable version of Android.
Fire OS starts with Android and adds
- cloud services (share reading on all Kindle devices),
- a content-forward user interface,
- built-in media libraries,
- productivity apps,
- platform enhancements to integrate Amazon's digital content and improve performance
- apps are from Amazon Appstore
- Current version is 3.5.0
- Quick Switch: Double tap the home button to show an overlay of all running apps so you can easily switch between them.
- Collections: Organize your apps and media items into dedicated folders, accessible right from the home screen grid.
- Accessibility features:
- Blind and visually impaired customers can leverage accessibility tools such as Screen Reader, Explore by Touch, and Screen Magnifier.
- Hearing impaired: Closed Captioning (when available in source), Hearing Aid Compatibility (HAC) rating of T4/M4, Stereo to Mono Audio
 5.4 release
In addition to Alexa, our next Fire OS update will also allow you to quickly access great game play directly from the Games tab with Twitch, the world’s leading social video platform and community for gamers. Fire Tablet owners will also have easy access to over 65,000 recommendations from ComiXology, which provides an unrivaled library of comic books, graphic novels, manga and more.