The SvxLink project is developing a flexible, general purpose voice
services system for ham radio use.
The SvxLink Server consists of a core that handles the connection to
the transceiver. The core can be configured to act as a repeater
controller or to operate on a simplex channel. The voice services are
loaded into the core as plugins.
The project also includes an EchoLink client GUI application (Qtel).

Opus is an optional (and, based on the audio quality, suggested!) 
dependency available from slackbuilds.org

You need a "svxlink" user and group:

 # groupadd -g 286 svxlink
 # useradd -u 286 -g svxlink -d /var/spool/svxlink -s /bin/false svxlink