Waiting for next Windows 8.1 successor , Windows 9 ? Maybe you cannot find any Windows 9 version, because Microsoft decided to skip Windows 9. Maybe Windows X want to chasing Mac OS X (same version right :p)
see What’s new in Windows X http://preview.windows.com
Quote from “http://blogs.windows.com/bloggingwindows/2014/09/30/announcing-windows-10/”
Start menu: The familiar Start menu is back, but it brings with it a new customizable space for your favorite apps and Live Tiles.
Everything runs in a window: Apps from the Windows Store now open in the same format that desktop apps do and can be resized and moved around, and have title bars at the top allowing for maximize, minimize, and close with a click.
Snap enhancements: You can now have four apps snapped on the same screen with a new quadrant layout. Windows will also show other apps and programs running for additional snapping and even make smart suggestions on filling available screen space with other open apps.
New task view button: There’s a new task-view button on the taskbar for quick switching between open files and quick access to any desktops you create.
Multiple desktops: Create desktops for different purposes and projects and switch between these desktops easily and pick up where you left off on each desktop. Find files faster: File Explorer now displays your recent files and frequently visited folders making for finding files you’ve worked on is easier.
Watch the below video from Joe Belfiore to see many of these features in action. Immediately you’ll see how Windows 10 carries forward a sense of familiarity, while providing new capabilities to help you way the work you want to and be more productive.