In beermaking: Chalk. Sometimes used for temporary hardness in dark beers. Adjusts pH up.
In winemaking: Used to lower acidity levels. 2.5 grams per gallon will roughly lower acidity by .1%. It does not require cold stabilization to precipitate-out acid like Potassium Carbonate does, but it takes longer, affects flavor, and it reduces tartaric before dropping out malic or citric acids.