Fruit in clusters, skin brownish green, glossy leaves. I've been assuming that these were crabs, but I found this growing next to a crabapple with smaller fruit, less glossy leaves, etc..
Bradford/Callery pear grow small fruit in clusters like that. Neither is really worth a crap for wildlife that I am aware of, but is planted everywhere for landscaping. May have been brought in by birds. Just keep an eye on them.....I'm not saying that is what they are, but looks very similar to me. Hopefully it isn't and it's something positive for you.