egg shell uses
Some people crush them very finely and sprinkle around plants to kill/deter slugs and other bugs.
I grind mine in an old blender, then put a spoonful or two in the holes where I'm planting my tomatoes. The calcium is said to ward off blossom end rot. So far, it works for me!
make sure to thoroughly wash them to get the membrane out before composting or adding to the garden. Animals will bee line for them if not.
I crush them in an old ziploc with a rolling pin or let kids stomp them in the bag. they WILL keep the slugs and cutworms off your cabbages and broccoli if you ring the plant with the shells. They don't like the sharp edges. Plus it is calcium for your plants!