Initially codenamed Windows Threshold, Windows 10 debuted on July 29, 2015, following a "technical preview" beta release of the new operating system that arrived in Fall 2014 and a "consumer preview" beta in early 2015.
With Windows 8 suffering from mostly negative reactions by both enterprises and consumers, Microsoft chose to eschew going with the logical next iteration of Windows, Windows 9, opting instead for the name Windows 10.
Windows 10 Drops the Unified OS Interface
While Windows 8 focused on presenting a unified operating system interface for all Windows-powered devices, from desktops and laptops to smartphones and tablets, Windows 10 presents more of a customized interface that recognizes the device's hardware and adjusts accordingly based on whether a mouse and keyboard are used or a touchscreen.
Windows 10 also reincarnates the Windows 7-styled Start button and Start menu that were dropped in Windows 8. The functionality for these features has been updated in Windows 10 with Smart Tiles and other dynamic capabilities.