Multi-User Voice Options

Here are a few of the main options for allowing voice communication while in a Multi-User Session:

Mumble: Mumble is an open-source, low-latency, high-quality voice chat software primarily intended for use while gaming. You can host your own server and users can join channels to chat.
As of SightLab 2.7 Mumble is installed with the SightLab installer (unless you uncheck it) and there are buttons on the server and client to automatically launch the server and client.

If running prior to Sightlab 2.7: Download the Mumble server and client from the links below. On the computer running the SightLab server, run the mumble server and for each client start the Mumble Client, press the settings to configure your audio (headset mic and headphones if using VR) and connect to the session with the same hostname as the SightLab server.

Download Mumble server and client from here https://www.mumble.info/downloads/

or direct links here (Note with the latest SightLab installer mumble can also be installed via checking the checkbox for Mumble)

Radmin, if connecting over separate neworks, the preferred method is using Radmin (see this page). Here is a page also on communicating with audio while connected with Radmin
https://radmin-club.com/radmin-vpn/how-to-chat-in-radmin-vpn/
Discord: You can set up a Discord server and have users join a voice channel while they're in a session. See here for how to use Discord for Audio
TeamSpeak: Similar to Mumble, TeamSpeak is a voice chat service often used by gamers. It's not free, but it offers high-quality voice chat and the ability to host your own servers.