I use iCircuit app all the time on my mac, which is a variation on Paul Falstad's circuit simulator (http://www.falstad.com/circuit/).
There are currently no objectives or any game element in DLS. I have some ideas on how this can be turned into a game. Haven't decided which of them will be feasible to implement and be (somewhat) fun at the same time.
I use iCircuit app all the time on my mac, which is a variation on Paul Falstad's circuit simulator (http://www.falstad.com/circuit/).