We have seen our relatives put a little egg shell in their coffee grounds as they make their morning coffee. According to them, this was done to take the bitterness out of the (probably cheap) coffee. This might be the use that most people are familiar with, but there are many more.
The calcium in eggshells allows the shells to be used for many different situations where some extra calcium is helpful – from supplementing your chicken’s feed to supplementing your own calcium. You may have heard of some of these uses, but you’re sure to find a few that are new to you!