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Mumble is a free, open source, low latency, high quality voice chat application.

Ziggs is a platform that exists to facilitate peoples communications. Smoothly Share Content Between Devices! Ziggs designed to facilitate communication in Schools, Meetings, Conferences, Workspace with channel name all agreed upon.

Zulip is an open source chat and collaborative software created by Jeff Arnold, Waseem Daher, Jessica McKellar, and Tim Abbott in 2012. Today, it is one of the free and open source alternatives to Slack, with over 40,000 commits contributed by 660 people.