Note: As of E-Learning Lab 1.1.11 you can now launch the Mumble server and client (if installed) directly from the "Advanced" Tools section
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. 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)
https://dl.mumble.info/latest/stable/client-windows-x64
https://dl.mumble.info/latest/stable/server-windows-x64
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.