From University of Minnesota, introduced in 1946, Malinda x Siberian crab. A very nice crab with nutty flavour, hardy to zone 3, mid season. A good grower, annually productive.
Picture from Claude's orchard: some Chestnut crabs from 2 different trees. On one they are larger, but on the other, they have better coloration. From my 2007 crop, harvested on Sept 8. Largest was 47 mm across (almost 2 inches).

GROWER COMMENTS:
Claude Jolicoeur, Quebec, Zone 4
A good variety in my orchard, ripens mid September and is very clean even if I don't spray. The flavor is great. Very recommendable as backyard tree.
hgforganicapples, Brian Caldwell, New York, Zone 5
This year in my orchard European apple sawfly is very heavy on my Chestnut crab trees. I think this is due to its early bloom. I like the flavor of this apple a lot! If it were a bigger fruit, it would be extremely popular in the marketplace.
Todd Parlo, Vermont, Zone 3
Has always obtained a favorable mention when I have had it at apple tastings. Chestnut Crab is just as popular at the Common Ground Fair in Maine with all us all-natural types. This makes this as good a place as any to note that if given a taste, smaller sized apples can be marketable. The audience to pay attention to here, however, is that of children. The apples that always get grabbed first by little hands are the really big ones, and the really small ones, among the latter have been pomme gris, centennial, and chestnut. They're cute, and attract the sort of crowd of adults too that go for those tiny bananas popping up in the supermarket. A little creative marketing might get folks to appreciate some really wonderful tastes, like that of the Chestnut with its wonderful complexity.
