My sister-in-law has these crab apple trees in her back yard and every year she picks a half bushel and makes crab apple jam and jelly. This stuff tastes great on pork and chicken or even on a bagel and toast with cream cheese.
I've made crab apple jelly before when I was living in Denver. The tree was part of the landscaping at my place of employment and the apples were going to waste. I picked them up, took them home and enjoyed crab apple jelly all winter long.