We have one blackberry plant, its a prickle-free plant and takes up what seems like no space as it just twirls around the other plants (and weeds!)
The Blackberries aren't as sweet and tasty as wild ones but they are still pretty good.
A few years ago we were given mini plum and apple trees as a gift. The plum tree has never so mauch as produced a blossom but the apple tree has a few fruits on again this year. They are both in huge pots and are tiny trees but the apples are full sized and lovely.
I'm not quite sure how you know when they are ready to pick, will have to find out as I don't want to loose them to drop and become a wildlife feast!