Zulip is described as 'The only modern team chat app that is designed for both live and asynchronous conversations. Zulip topics create a separate space for each discussion, so different conversations will never get in each other's way' and is a very popular instant messenger in the social & communications category. There are more than 100 alternatives to Zulip for a variety of platforms, including Android, iPhone, Web-based, Windows and iPad apps. The best Zulip alternative is Signal, which is both free and Open Source. Other great apps like Zulip are Telegram, Element, Discord and Matrix.
Kwayet is an internal communication app exclusively for your team or workplace. You can collaborate, call and message anyone without requiring a phone number.?
Online team collaboration - secure video conferencing, document sharing, chat, e-signing, expense tracking. Free and paid subscription.
signal-cli is a commandline interface for the Signal messenger. It supports registering, verifying, sending and receiving messages. signal-cli uses a patched libsignal-service-java, extracted from the Signal-Android source code.
BBM Enterprise enterprise messenger offers faster communication, collaboration and decision making while providing enhanced security over corporate data.
Valour is an open-source, privacy focused alternative to platforms like Discord or Slack, developed by a small team of volunteers. The app has been in development for over three years and is currently in it's alpha stages of testing.
Offers free global video and voice calling, group chat with up to 50 participants, in-app messaging that bypasses SMS plans, music clip sharing via Spotify, photo editing, gaming and gifts, animated messages, mini-games during calls, and centralized media gallery.
Smoke Messenger is an open-source Instant Messenger that is known as the first mobile Messenger worlwide using the encryption algorithm McEliece. To be downloaded at F-Droid.org or Github.com. Smoke provides with its own Server-Software: SmokeStack-Echo-Server.
HeyTell is an "Instant Voice Messaging" system that allows users to connect in a manner similar to a push-to-talk radio handset. It supports different privacy levels as well as a friends list and geolocation.
Slenke is an internal social network for your company to securely communicate, share files, manage projects, organize tasks, track time and more. View updates and keep track of whats happening at the workplace no matter where you are.
Gone are the days of needing to make a whole bunch of different tools work together. With Circle, you can combine the exciting, interactive nature of a community with your content — all in one seamless experience.
Team communication without the noise and distraction of instant messaging. Messages are sent on a fixed two hour schedule, giving plenty of time to get into deep work and flow.
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.
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