Technically Mangaves are actually Agaves (at least that is their current botanical name), so here is fine. I think somebody started a thread dedicated to that group but it has not had a lot of traffic.
To explain, the name Mangave derived from the old nomenclature. It was an intergeneric hybrid:
xMangave = Agave x Manfreda (the latter often with purple spots, which are inherited by the hybrid)
But Manfreda was lumped with Agave and no longer exists as its own genus, so they are all Agave hybrids now. The name Mangave remains descriptive and quite useful, especially as it pertains to the purple coloration.