Software to assist with book loans for a public library

We've launched a sharing system in southern Ecuador (Vilcabamba, Loja) which offers the ability to borrow books from a library as a membership benefit. But we are trying to use the plain exchange system for that, for lack of a better option, and that is slow and cumbersome. Does anyone know of a real library system, that will provide book inventory/lookup, and track usage for 5,000-10,000 books? We've looked at Millennium, but can't get it to work. Thanks!