Ubuntu used to use the GNOME 2 desktop environment, but it now uses its own Unity desktop environment. The Ubuntu project has a focus on providing a solid desktop (and server) experience, and it isn't afraid to build its own custom technology to do it. Much of the software in these repositories is synced from Debian's repositories. Ubuntu is based on Debian, but it has its own software repositories. Ubuntu is probably the most well-known Linux distribution.

You could also use Linux From Scratch to compile and assemble your own Linux system from the ground up, but that's a huge amount of work. If you want to 'install Linux,' you'll need to choose a distribution.