"If you truly wish to relinquish ALL rights then public domain is exactly that. This is obviously the most free. If additionally you wish to retain attribution only then /usr/src/share/misc/license.template is a great choice. This is probably the most free except for public domain. If it bothers you if Microsoft uses your performance in a Vista ad then you must pick something else. But now you are in a sticky place where you want to share except when you don't. The available licenses are tricky legalese, and finding one to match your motives is difficult and the license may have consequences you don't anticipate."