Windows NT 5.0
Windows 2000 is still considered one of the best versions of Windows to have ever come out.
It is built on the stability and scalability of the Windows NT platform. That means that Windows will continue running for weeks or months without requiring a reboot, or a poorly written program crashing the entire operating system.
Besides having great stability, it also supported the latest hardware and technologies such as FAT32, NTFS, USB, AGP, and WDM.
And then on top of all that, it had great gaming technology support. It worked with the latest OpenGL and Direct3D games.
Even today, you will find many people still running Windows 2000.