lots of customizations and some shell modifications. for and example, windows has an feature called Custom Shell that allows you to use other shell replacement (like cairo shell and blackblox for an example)
to use those features, you need to enable the "Custom Shell" feature in the Optional Features window
(Win+R then "OptionalFeatures")
after it, you need to download the replacement that you want:
Examples:
Cairo desktop environment
LiteStep (Windows 8/8.1/10 isn't fully supported by it)
BlackBox for Windows (Windows 8/8.1/10 isn't fully supported by it)

you also can use a custom WM like Hash Tiling Window Manager for an example, but it only supports windows 7 (like most part of the custom wm availables for windows)
here a list of the available WM's for windows:

https://www.slant.co/topics/1249/~best-window-managers-for-windows (for blackbox, I recommend the bug.n ones)