The Wikipedia entry Gratis versus libre contains the following text:
Libre /ˈliːbrə/ in English is adopted from the various Romance languages, ultimately descending from the Latin word lībere; its origin is closely related to liberty. It denotes "the state of being free", as in "liberty" or "having freedom". The Oxford English Dictionary (OED) considers libre to be obsolete, but the word has come back into limited use. Unlike gratis, libre appears in few English dictionaries, although there is no other English single-word adjective signifying "liberty" exclusively, without also meaning "at no monetary cost".
If there truly is no such word, then I must grudgingly accept the ugliness of Libre. I must admit that nothing springs readily to mind. Is there such a word?
EDIT: The basis of this question is that the people who coined (or revived) the term Libre didn't do so lightly. They were obviously of the opinion that it was necessary.