If Experimental Interface and Push The Limit are both equipped to a ship, they can be used together to perform two additional free actions. After the actions have resolved, the ship receives 2 stress tokens.
Experimental Interface is unique. Some copies were printed without the • (unique symbol) in front of the name. (X-Wing FAQ, v 3.1.1, 07/24/2015; v 3.2, 09/04/2015)