Are there any open source libraries/projects which work in a similar way to http://www.tagattitude.fr/en/products/technology?

I am trying to understand the process. At first I thought this could work like when you send a fax to a fax machine.

It is basically using the mobile phone’s microphone as a captor and its audio channel as a transporter.

Are there any libraries for generating the signal and then being able to decode it?