Why Unity is named as "Unity"? Is there a philosophy behind Unity's name or is it just a normal naming?
The Unity project started by Mark Shuttleworth and Canonical has gone on to deliver a consistent user experience for desktop and netbook users alike. Putting great design at the heart of the project, Unity and its technologies such as Application indicators, System indicators, and Notify OSD, have strived to solve common problems in the Free Software desktop while optimizing the experience for touch, consistency and collaboration.
The idea behind it is to "Unite all devices into one common interface", be them TV, Smartphones, Computers, Netbooks and anything new that comes. This is why the Unity interface is similar in any device it is installed to.
Unity can be extended to others Distros. For example Fedora and OpenSuse are thinking of having Unity as a Desktop option. Archlinux is working on having it added.
So in a way, Unity is a Interface that will unite different Devices and also have a common Interface between Distros in the future. When I say common, I mean that Unity can be found as an alternative or maybe the default desktop in other Distros.
For Distros that already have working implementation of Unity:
Leeenux - http://www.leeenux-linux.com/ ArchLinux - Has Unity in the repos.
For Distros that are working on implementation Unity:
OpenSuse & Fedora - Had some work with it. They have it on hold until Compiz and some bugs are taken care of.