For a nice, polished, non-skeuomorphic circuit simulator, see iCircuit [1], which provides native MacOS and iOS clients (based on the Falstad JS circuit simulator mentioned elsewhere in this thread, if I recall correctly). It differs from most SPICE-based simulators in that there is no edit or run mode - the circuit is always simulating in transient mode so updates happen in real time.
[1] https://icircuitapp.com/