Android (operating system) and rival Linux mobile operating systems that were in development. These established players were skeptical: Nokia was quoted as saying "we don't see this as a threat," and a member of Microsoft's Windows Mobile team stated "I don't understand the impact that they are going to have." Since then Android has grown to become the most widely used smartphone operating system and "one of the fastest mobile experiences available". Reviewers have highlighted the open-source nature of the operating system as one of its defining strengths, allowing companies such as Nokia (Nokia X family), Amazon (Kindle Fire), Barnes & Noble (Nook),
Smartphone when the cover is closed, it protects the screen. Some "book"-like cases have additional pockets for credit cards, thus enabling people to use them as wallets. Accessories include products sold by the manufacturer of the smartphone and compatible products made by other manufacturers. A mobile operating system (or mobile OS) is an operating system for phones, tablets, smartwatches, or other mobile devices. Mobile operating systems combine features of a personal computer operating system with other features useful for mobile or handheld use; usually including, and most of the following considered essential in modern mobile systems; a touchscreen, cellular, Bluetooth, Wi-Fi