iOS (formerly iPhone OS) is a mobile operating system based on macOS and on components of the Mach microkernel and FreeBSD, a Unix-like operating system, developed by Apple Inc. exclusively for its smartphones. It was unveiled in January 2007 for the first-generation iPhone, launched in June 2007. Although some parts of iOS are open source under the Apple Public Source License and other licenses, iOS is an Apple proprietary software. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also includes the system software for iPads (predating iPadOS, which was introduced in 2019) as well as on the iPod Touch devices (which were discontinued in mid-2022).[14] It is the world's second-most widely installed mobile operating system, after Android. It is the basis for three other operating systems made by Apple: iPadOS, tvOS, and watchOS. Since its launch, iOS has been extended to support other Apple devices such as the iPod Touch (September 2007) and the iPad (introduced: January 2010; availability: April 2010). As of December 2023, Apple's App Store contains more than 3.8 million iOS applications. These mobile apps have collectively been downloaded more than 130 billion times. Major versions of iOS are released annually.