minimodem - software audio Bell-type or RTTY FSK modem
Copyright (C) 2011 Kamal Mostafa <kamal@whence.com>
Minimodem is a command-line program which generates (or decodes) audio
modem tones, emulating an old Bell-type or radio-teletype FSK modem.
The tones are played to (or recorded from) the default system audio
device or a file.
Minimodem can be used to transfer data between nearby computers using an
audio cable (or just via sound waves), or between remote computers using
radio, telephone, or another audio communications medium.