I have been messing with using the Arduino and FlowStone to produce an "experimental" oscilloscope.
The problem right now is that I don't have a good signal source to use (and fingers around a wire doesn't prove much!
Please try this out and see if you can improve the results (hopefully, by someone with some real test equipment!)
(AD0 is the Arduino input, just load the sketch into the Arduino, load the FlowStone program and turn on the upper switch on the Arduino/Flowstone interface module in the FlowStone program. It seems pretty stable, but it is pre-alpha quality...)