<unk>  is the calcium salt of citric acid.  It is commonly used as a food additive (E333), usually as a preservative, but sometimes for flavor.  In this sense, it is similar to sodium citrate.<unk>  is also used as a water softener because the citrate ions can chelate unwanted metal ions.<unk>  is also found in some dietary calcium supplements.
Calcium citrate
Potassium citrate
Calcium sulfate
Magnesium citrate
Calcium acetate
Potassium salicylate
Strontium ranelate
Magnesium aspartate