Gapp's low altar is an altar in Gapp's temple on Street of Small Gods (SE from Drum), n,n,e,s from temple entrance.

If you place any item of clothing on this altar, it will be fixed. Your faith GPs are used for fixing, and if you don't have enough, item will be fixed only partially.

It is possible to pick item that someine else placed on altar, but it is illegal by AM laws and definitely not wise thing to do. Anyway, better pick your own item fast after placing on altar to avoid confusion.