Housing NPCs

What do they do? The mender's obvious, but I'm not sure what the rest do.

Junkmonger sells dyes, overpriced brooms, garden patches and dark matter.
Material supplier sells misc materials used for crafting.
Mender mends gear.
Servant sells snacks and housing items.
Materia Melder melds materia (open slots only, overmelding via npc is not permitted)

Thanks much!