Though not explicitly a Marxist work, The Crucible is nonetheless amenable to a Marxist interpretation. What's notable about the Salem witch craze as depicted in the play is the way that a previously downtrodden, marginalized figure—Abigail Williams—comes to achieve a remarkable degree of power in such a short space of time.
Even though it's not her intention to do so, Abigail effects something of a social and political revolution in town, overturning the old order and giving herself a voice. In the midst of such a toxic environment, it doesn't matter how wealthy or well-connected you are; you can find yourself dangling on the end of a rope on a trumped-up charge of witchcraft if Abigail decides to point the finger at you.
In a Marxist interpretation, one could argue that Abigail represents the proletariat, taking control of the legal machinery of the state in order to bring about a revolution. The judges are supposed to be in charge of the judicial proceedings, but in actual fact they're dancing to Abigail's tune. She's the one in control, not them—no mean feat for a young girl previously despised and marginalized by bourgeois society.
Abigail's theft of her uncle's money could also be interpreted—in the broadest possible sense, of course—as a representation of the proletariat taking control of the economic means of production.