Coventry is a IP telephony server for connecting SIP devices and softphones with advanced voice, messaging, and facility automation services for gnu/linux that is optimized for running on small servers such as Raspberry Pi, and possibly even routers.

Finally, I have drafted a full feature description for Coventry, which really includes next years goals.

https://codeberg.org/gnutelephony/coventry/wiki/Features

coventry

Coventry is a residential and small office IP telephony gateway for use on small linux servers and even routers.

^Codeberg.org