Not Cambridge, but Ron's Ice Cream & Bowling in Hyde Park and Dedham have incredible frappes. Fantastic family owned business, I've been going my entire life.

My dad first went in the 80s and asked Ron for a milkshake. Ron looked at him, took a cup, shook up some milk, and handed it to him. It was then that my dad from central NY learned that New Englanders call "milkshakes" frappes.