Which operating system did Microsoft release in 2015?

Microsoft released the Windows 10 operating system in 2015. It became generally available on July 29, 2015, as the successor to Windows 8.1.

Windows 10 marked a shift away from the strongly tablet-oriented interface of Windows 8. Microsoft brought back a redesigned Start menu, while also introducing features such as the Cortana assistant, Task View, virtual desktops, Action Center, Windows Hello, and the Microsoft Edge browser.

Microsoft promoted Windows 10 as “Windows as a service.” Instead of relying only on occasional major releases, the company delivered ongoing feature and security updates through Windows Update. Eligible users of Windows 7, Windows 8, and Windows 8.1 could upgrade free during the initial offer period.

A common mix-up is Windows 11, which arrived later in 2021. Windows 10 was also associated with the development codename Threshold, but the question asks for the released operating system, not its internal project name.