The list of universal hymns of Catholic people has settled into a solid 50 chants that constitute an essential foundation of sacred music shared by Catholics in all places and times, the music that you will need to know to participate in international liturgies and the music that holds up over time, from season to season, to be sung by the people (schola exclusive chants are not in the list). They are all peoples' hymns, and though some are harder than others, none should be too difficult for non-musicians, provided they are heard and sung enough.
They also happen to be the basis of a vast amount of musical exploration in the 16th century and following and so constitute the basis of the modern Western musical tradition. Here is our real "folk" heritage.
There may be readers who know them all; most readers of this blog will know perhaps half. As a result of grave neglect and diversion for several decades, most American Catholics know none (I guess on my part). Is there anyone who would say that this is a good thing?