What it does is to act as a SIP softphone, and spawn a process for each incoming or outgoing call, which can handle events (like DTMF tones) or do actions (like playing files) via stdin/stdout.
Currently, I am using it to spam filter incoming calls at home.
As a side question: I wonder where one can publish software like this nowadays, when freshmeat etc. are either gone or read-only. Preferably a place that is not GitHub.
https://sourcehut.org/ is what I recommend for publishing code when one doesn't want to use GitHub/etc.
The last one looks like it has too many features for my taste, but I will keep it in the back of my mind (or rather: my bookmarks) if I'm ever in need of something along the lines of GitHub.
Please consider adding a license.
Thanks :)