Linux

It's main purpose is to demonstrate how Linux could function with a less unix-like file structure, in an effort to make it more intuitive to use, and to make it possible to have multiple versions of a library/package without conflict.

I personally really love what they attempted, but it's unfortunately not been adopted anywhere else, making it unpractical to use as a daily driver.

But it serves as a very successful experiment that hopefully someday inspires change or a new way of thinking about the Linux file structure for other distros.