MultiMode Lite for Mac

From Black Cat Systems:

Allows your Macintosh to decode many different modes of non-voice communication often heard on shortwave and ham radio. It is the only program of its kind for the Macintosh, rivaling commercial packages for the PC platform costing hundreds of dollars. It is ideal for amateur radio operators, shortwave radio listeners, and other radio enthusiasts. MultiMode Lite allows you to decode and display RTTY, CW, & FAX without any extra hardware. In the past, dedicated hardware, often costing hundreds or thousands of dollars, was necessary to demodulate and decode this transmissions. Today, you can use the processing power of your Macintosh to decode and display these modes, without any extra hardware. Just connect your radio's speaker output to your Mac's microphone input, and you're ready to go.