Windows 7
Windows 7 is the successor to Windows Vista
What is Windows 7?
Windows 7 is the successor to 
Windows Vista . The new OS introduces a compelling combination of welcome innovations and much-needed polish. Windows 7 is built with the codebase from Vista and is a minor upgrade (6.1) in the NT series of operating systems from Microsoft. Windows XP Mode and Windows Virtual PC, available ONLY on Windows 7 Professional and Windows 7 Ultimate, allow you to run multiple Windows environments, such as 
Windows XP Mode , from your Windows 7 desktop.
All editions of Windows 7 can make System Images without additional system backup programs, which were necessary for system backups of Windows XP or Vista.
Windows Vista . The new OS introduces a compelling combination of welcome innovations and much-needed polish. Windows 7 is built with the codebase from Vista and is a minor upgrade (6.1) in the NT series of operating systems from Microsoft. Windows XP Mode and Windows Virtual PC, available ONLY on Windows 7 Professional and Windows 7 Ultimate, allow you to run multiple Windows environments, such as 
Windows XP Mode , from your Windows 7 desktop.All editions of Windows 7 can make System Images without additional system backup programs, which were necessary for system backups of Windows XP or Vista.
Discontinued
Mainstream support for Windows 7 ended on January 13, 2015. Extended support with security updates ended on January 14, 2020.
IMO
The last (as of writing this) version of Windows that does not streamline itself to the point of being difficult for power-users to control the system on a low level.
Most Popular Windows after XP, it has glass aero features and have no bloatware and metro apps
I used to like Windows but after some time using it, I'm starting to hate it because
1)cannot completely remove Internet Explorer,Windows Media Player,Paint,etc which takes some space in my small hard drive
2)too many maintenance and apps needed to optimize Windows 7
3)a pain to find driver after clean install
In my opinion,Ubuntu is better than Windows 7 (never tried Mac yet)
Better than windows vista also windows 8
but why they removed aero on windows 10 is beyond believe
It has option disable desktop composition then you have classic theme, low input lag
My Childhood Would never been the same without Windows 7
R.I.P. Windows 7
MS Windows is never going to be same if it's not Windows 7.