An Open Source Multimeter would be an interesting project. But I wouldn't expect to see a rotary switch on it. Rather, I would expect it to use new techniques like CTMU (Charge Time Measurement Unit). Most measurements could be made by just connecting the device to a part or to points in a circuit. It could detect a component and report resistance, capacitance, inductance, beta, etc. If connected to an active circuit it could detect voltage, current, phase, frequency, duty cycle, etc. and report ... all without the user turning a single dial. Maybe the user would press a start button ... likely built into a probe. It could have an audio annunciator so the user wouldn't have to take his eyes off what he is doing. It could take voice commands.