If so, you can become a Windows Insider and join their program to preview Windows 10. Yes Windows 10. They have decided to skip Windows 9 and go right to 10. There are many theories floating around the web about it. One is that it wanted to get as far away from Windows 8 as it could; another is that older programs made for Windows 95 or 98 could get confused with 9. Someone else jokingly said it was using the logic of this video.
The Windows 10 OS is yet unfinished. Why would they ask you to download it? To help give feedback for development. You can have a say as they progress before their 2015 release (TBD) through their feedback app. You should use a secondary PC you aren’t using anymore for this because it isn’t ready for production.
Some of the new features highlighted are:
Return of the start menu
Live tile preview on the side
Return of search box
Improved app store
Snapping windows is easier (up to 4 apps on a screen)
Separate desktops (for work/home for example)