Not that the adjoining cities of Boston, Cambridge, and Somerville have a public transit system that covers all completely (or indeed that even what falls under Boston is comprehensive to some areas with respect to the subway) but the Boston metro does have some form of transit that covers the area within the metro proper--past which it peters out aside from commuter rail--which is decent but which mostly functions as, well, commuter rail.

Boston is no denser than Tokyo, and compared to European capitals, very underserved by mass transit. The MBTA is a shitshow and it is fairly unusable as a reliable means of transportation.