MacCRO is a simple, easy-to-use oscilloscope and spectrum analyser for the Macintosh. It is limited to audio frequencies (usually 22.050kHz or 44kHz, depending on the model of Mac being used), but it has a major advantage over a "real" oscilloscope: cost. While a typical, cheap 20MHz scope may cost a few hundred dollars, MacCRO is only US$20 shareware. It can also save data into image or text files.

MacCRO