Jitsi Desktop (previously SIP Communicator) is a legacy audio/video and chat communicator with full encryption, precedessor of Jitsi Meet .
Jitsi Desktop is not actively developed anymore: last version, released in October 2017, can be still downloaded from GitHub. Its successor is Jitsi Meet
Skype is the most popular free voice-over IP and instant messaging service globally. It allows users to text, video and voice call over the internet. Users can also call landlines and mobiles at competitive rates using Skype credit, premium accounts and subscriptions.
Wire is the most secure collaboration platform featuring messenger, voice, video, conference calls, file-sharing, and external collaboration –all protected by the most secure end-to-end-encryption.
Zulip is a group chat app in which messages are threaded by topic, helping you have long-running, organized conversations. Zulip's threading makes it easy for people not always on chat (like managers, remote team members, contractors, part-time workers, etc) to weigh in on...
Video conversations with up to 8 people in your browser - no downloads, no login. Just name your channel and you are on. Works in all modern browsers, even mobile.
Nertivia is an chat client that allows you to chat to anyone across the world. There are a lot of features that don't require you to pay at all such as, gif profile pictures, free custom emojis and more coming soon!
Zoiper IAX & SIP multilanguage and multiplatform (Windows, Linux and Mac OS X) softphone is a VoIP soft client, meant to work with any IP-based communications systems and infrastructure.
Fully open source instant messaging server and clients. No proprietary components or non-free dependencies. Backend in pure Go (GPL 3.0), with a command-line administration tool in python + gRPC. Clients for Android, iPhone, and Web - ReactJS (all licensed under Apache 2.0).
An encrypted instant messaging with video call and GPS features for android.