What version of Linux is with AsteriskNOW?

It states on the AsteriskNOW main page that it’s a customized linux distribution.

What version of linux is it based on?

To what extent is it customized? It is just that it has asterisk added to it, or is it ‘a fork’ of the distribution?

Thanks

Right now I think asterisknow `1.5-beta is using centos, and it uses regular asterisk packages, they just add the gui ontop of it
the 1.0 version uses rpath