Really any kind of cleaning you might use a paper towel or sponge for
Mopping up spills
Washing the car
Protection against bedwetting/menstrual overflow/puking/whatever
Cut into strips and use as stuffing for something like teddy bears or doll pillows or cat beds
Protecting the floor when DH is brewing beer
Stuffing leaky windows
Attic insulation...okay, I'm stretching there, but theoretically possibly I guess!
We reuse those diapers until they are absolutely falling apart...and then we use them some more! lol Makes me feel better when I insist on buying nice fluffy new ones for each new baby.