I've been getting Starbuck's used grounds for my plants for a long
time. They do make good mulch but use sparingly. I also find that
they tend to contain flies (maggots) and gnats so you might want to
bake it before spreading it on indoor plants.

Vermicomposting is great indoors. I kept a stack of 5gal rubbermaids
under my kitchen sink without any troubles. To prevent smells, make
sure your brown:green=3:1 by weight. You have to take the whole thing
outside once a month and to pour out the drip tray and let the bottom
tray breath. Worms love coffee grounds.