Had when i worked in a preschool and kids love them! I would use colored sand instead of white salt. DIY salt tray with alphabet cards. Easy to make and kids have fun smoothing out the salt after correctly making the letter
Clothespin Math on a clothes hanger! Easy to make, and self explanatory. I'm thinking a wire clothes hanger would work better, so the clothes pins are easy to slide back and forth (almost like an abacus).