Tox is described as 'With the rise of widespread government monitoring programs, Tox is an easy to use application that allows you to connect with friends and loved ones without anyone else listening in' and is a leading instant messenger in the social & communications category. There are more than 100 alternatives to Tox for a variety of platforms, including Android, iPhone, Windows, Linux and Mac apps. The best Tox alternative is Signal, which is both free and Open Source. Other great apps like Tox are Telegram, Element, Discord and Jami.
Skred is the first secure peer-to-peer instant messaging app - No need for an email address or phone number to use it.
Skred is free, without subscription, without a provider, without a SIM card, and without leaving a trace.
Antox is an Android client for Tox. It aims to bring the full multimedia support Tox offers to your device, although it's still currently in heavy development.
Off-the-Record (OTR) Messaging allows you to have private conversations over any instant messaging (MSN,Gtalk, Facebook and so on) by providing encryption, authentication, deniability, perfect forward...
This project won the first prize 🥇 at Telegram Lightweight Client Contest and now is an official Telegram client available to anyone at web.telegram.org/a.
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.
Bitmessage is a P2P communications protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities.
SchildiChat is a Matrix client based on Element with a more traditional instant messaging experience.
Kaidan is a simple, user-friendly Jabber/XMPP client providing a modern user interface using Kirigami and QtQuick. The back-end of Kaidan is written in C++ using the QXmpp XMPP client library and Qt 5.
monocles chat is a fork of blabber.im and Conversations with some changes, to improve usability.
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Just a mechanism for encryption, and as such part of or plugin for other chat tools (for instance, Pidgin and Adium).