I agree with Yoderjac on the first page voting for a bird-sized crab apple tree. I have two at our home, and the one variety I'd recommend is the "Sugar Tyme" crab apple. It's very highly rated for disease resistance, gets covered in white blossoms in spring, and puts on 3/8" dia. red crab apples that hang on into winter. Fall leaf color is orange-ish yellow. Birds love to eat the small apples all winter. The tree is reportedly a smaller tree in size, which is another reason I planted one at our place.
Sugar Tyme is on the "favorite" lists of several crab apple breeders and horticultural professors at various universities. It's an award-winning tree. FWIW.
Not necessarily trees for small spaces - but if anyone likes great fall color from maples without the "helicopters" to spread unwanted seedlings, I can suggest two dandies.
Sun Valley red maple - seedless male selection. Nice red fall color, upright oval shape.
Autumn Spire red maple - seedless male selection. Red, orange-ish/red fall color, upright oval shape.
I've had the Autumn Spire red maple planted in our front yard for 5 or 6 years now. No "helicopters", great color, and it shapes itself. My wife and I love it.