What's the difference between the Liber Usualis and the Graduale Romanum?

This question has plagued yours truly for some time and Deo gratias, this resource came just in time to the rescue. See the List of Uniform Titles for Liturgical Works of the Latin Rites of the Catholic Church.

This list gives a comprehensive listing of pre and post-conciliar liturgical books in the Latin rite, including the rites of the religious orders and other such variants.

Thanks to NLM for the info.