Kokkocynips rileyi on Scarlet Oak/Quercus coccinea. A new paper says the caps on these attract ants.This looks like it might be another Kokkocynips rileyi. On Northern Red Oak/Q. rubra.Zopheroteras guttatum on Shingle Oak/Q. imbricaria.Some of these are awfully small. Zopheroteras sphaerula on Red Oak/Q. rubraAndricus quercusstrobilanus on Swamp White Oak/Q. bicolor.They look like they might be chewy, but are actually quite hard.Philonix fulvicollis on White Oak/Q. alba. “On” except these had already fallen off the leaves and were underneath this majestic tree. Andricus dimorphus on fallen White Oak leaf.A lot of these are detachable and end up on the ground.
Backyard and Beyond 
Great photos of a fascinating phrnomenon! Thank you for identifying these galls!