I believe they're often pickled or made into jellies.

Crabapples are more useful than apples actually.

They can be used for many of the things regular apples are, and are better than the latter for things like pickles, jellies, and hard cider. Plus they can be used as rootstocks, wildlife food, and ornamentals. They are usually much more dependable bearers as well, producing when full-size apples are frozen out, etc...

BUT, 99% of the crabapples planted in this country are purely ornamental/wildlife trees! They are mostly inedible and only can be used for a few of the things mentioned above...

Also see the related post on "crapapples"!

A crabapple question. I am seeing a lot of them around. Are they all crabapples or is there another look-alike that some could be? I see a lot of them with fruit the size of a Montmorency cherry.

THere are crabapples the size of a small blueberry. Apples are probably the most diverse fruit we grow. There are many varieties of edible crabapple. They are great to have as a branch in your tree because they're so good at pollination. They are more nutritious by weight than regular apples.
John S
PDX OR