What can broken egg shells be used for?

Some useful uses for eggshells:

Garden mulch.
Use eggshells to start seedlings indoors.
Nourish your tomatoes with a boost of calcium.
Add powdered eggshells to your foods.
Kick the pests out.
Make a natural abrasive cleaner.
Use eggshells to deter slugs and snails.
Make a calcium-rich supplement for your pets.
Use eggshells to make a natural dye for Easter eggs.
Use eggshells to make homemade sidewalk chalk.