Port the Analog Electricity activity.
This one is requested very often, so we really need to get it back at some point.
Also, some comments from a user requesting a few improvements to it:
"it would be cool to add some components in the future:
adjustable resistor, capacitor and inductor, diode, one small signal NPN and PNP transistor, relais, loudspeaker (-> sound).
And a dream would be a simple oscilloscope with self-adjusting scales."