You can substitute them for regular apples IF you compensate with enough sugar or honey to counteract the sourness. And of course they are a pain in the next to peel because they are so small. Growing up, we just made jelly with them, but you can use the crab apple jelly as a base and layer in other flavors, too - mint, herbs, other fruit ... quince ...

The best use for crab apples was always chucking them at one's brothers ... or neighbors ...