All the major unix versions in the market are not free, that means you can't see the source code.
You may want to check out FreeBSD or OpenSolaris OR you may want to check out linux distros.
Almost all linux distros are free and you can check out the source code.
The link provided by porter is about
GNU...It's all about open source movement.
I guess you didn't get the context of his message.
Ravinandan