Free open source end-to-end encrypted peer-to-peer calling and messaging app. It supports video calls, audio, messaging and has a Skype-style interface. It has apps for all major platforms including Android, iPhone/iPad, Linux, Mac and Windows.
Federated free open source communications platform with support for messaging and calling. The platform has many different apps available with the most popular being Element (formerly known as Riot).
Develops and maintains the XMPP standard for instant messaging and voice and video calls. It’s a free open federated standard, so anyone can set up their own server or write their own app. (XMPP used to be known as Jabber.)
Free open source packet analyser software, used for network troubleshooting and development.
A free open source video conferencing site which aims to provide a privacy-friendly alternative to proprietary services. Calls are made through the web browser using the BigBlueButton platform.
Fediverse address (in German and English):
Free open source XMPP/Jabber app for Linux which includes support for end to end encrypted messaging, voice/video calls and conferencing.