They are very good as de-odourizers, we use them in the kitchen and sometimes in a small perforated plastic container in the footwell of the backseats in our car.
The fragrant smell lasts a long time also surprisingly.
Also it seems to be useful in fridges too.
That link lists the following:
- Deodourize fridge
- As a scouring agent
- A cheap varnisher
- Dye for paper
- Promoting Hydrangea health
- Ash absorber
- Exfoliant
- Cockroach trap
- Fortifying plants
- Compost
So the above is quite a good list of uses that could be applicable for your situation
I just found 34 uses here too, I have to say though that using ground coffee as a method for salting a path didn't work for me.
Additonal uses:
- slug killer
- mushroom grower
- carrot and radish feed
- worm attractor
- cat deterrant (this didn't work for me)
- play doh dirt
- make a pin cushion
- garbage disposal cleaner
- drain cleaner
- add weathering to wood
- meat tenderizer
- make energy bites
- egg dyeing
- coffee candle
- make fossils
- treasure stones
- paint
- flea bath
- remove build up from hair
- eye bag remover
- deodorizing salt
- salt scrub
- face mask
- path/road ice melter