Crushed egg shells have many uses:
Garden Fertilizer
Eggshells are rich in calcium and other minerals that help your garden. Add a little ground egg shell into each hole before planting. Sprinkle some shells around the base of your plants every couple weeks.
Give your tomatoes a calcium boost. with ground egg shells.
Ground eggshells make a good non toxic cleaner for pots and pans, just mix a little soapy water.
It’s almost impossible to get a scrub brush down the narrow neck of your thermos. Rinse with hot water, then add some ground egg shells, fill halfway with water and shake. The shells will act as an abrasive and remove mold or other stuff built up on the inside.
Pest Control
Scatter crushed or ground egg shell vegetables and flowers to help keep slugs, snails, and cutworms away from them. They don’t like crawling over the sharp pieces of shell.

House Plants

Keep a jar of eggshells covered with water for watering your indoor plants.

I also feed them to my chickens as a calcium supplement.

There are many more uses for ground or crushed egg shells, these are just a few examples.