A simple DTMF/MF synth running in the terminal, using JACK for audio output. If you pass it -f it uses MF tones, otherwise DTMF. The number keys map to their respective keys on a phone. A-D, *, and # as well for DTMF. In MF mode, ST3 maps to 'a', ST2 is 'b', KP is 'c', KP2 is 'd', and ST is 'e'.