Very little of the free software in the world is "Public Domain".
Public Domain means that the author(s) have given up the copyright and all rights to the software. This means that you can do anything with it, including making a small change and start selling it as your own software. This is very rarely done these days, so there's very little Public Domain software around.
Open Source software is usually protected by some form of license, like e.g. the Gnu Public Licens (GPL), and is not in the Public Domain but quite often "free" as in beer as well as free in the sense that you're allowed to modify it.
Proprietary software can also be "free" as in beer, i.e. gratis.
As for free LightScribe labeling programs, I only know of the two that The Kipper has already mentioned.