From what I read, a big part of the drug trafficking in Boston goes through street gangs these days. There are unaffiliated Dominican drug trafficking groups active in for instance Boylston Street or Mozart Street. Puerto Rican drug gangs (mostly Latin Kings) are all over New England and they also operate in Boston. Neighborhoods like Dorchester and Roxbury have a lot of Cape Verdean gang activity; the Cape Verdeans seem to push a lot of dope as well as amphetamines.

More traditionally speaking, the New England Mob is still active as well, Chinatown no doubt has some Chinese gang activity and bikers are around as well (Hells Angels, Pagans...there actually was a noteworthy Pagans bust some time ago).