Charlie's is essentially a lunch counter with some tables. It reeks of Boston's past, not in that ersatz chain manner but the real past. It's true that black musicians who used to play the jazz clubs would come to Charlie's but so did cops and politicians and everyone in the neighborhood.
The food is good quality diner. I have a particular fondness for the turkey hash. The french toast is also excellent. But the main thing is that when you're in the place, you know you're in a real place.
Near Mass Ave. Not open late. Very hard to park around there.