More like this
There are many versions of Linux, but the two biggies seem to be Debian (on which Ubuntu and many other distributions are based) and Red Hat. Red Hat uses a commercial support model, so it is an example of a very different approach than Ubuntu.
I had promised a little more info on Scientific Linux. This is a form of Linux with a name that changes faster than my shirt when I realize I've got it on inside out. Form the Fermi LInux site:
This weeks Pseudoscie