Torchat!

Riot (formerly Vector) is an opensource interoperable app running on Web, iOS and Android. It is built around chat rooms, both public and private and provides messaging, filesharing, voice and video conferencing (beta on Android and web), integrations to tools like GitHub, Jira, Jenkins and much more soon. Vector is built on the Matrix.org open standard which provides bridges to other systems such as Slack, IRC and a lot more soon. One can use the hosted service or run their own. »

RetroShare is a open source cross-platform, private and secure decentralized communication system. It lets you to securely chat, share photos, videos, and more, using OpenPGP to authenticate peers and OpenSSL to encrypt all communication.

ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.

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. It uses strong authentication which means that the sender of a message cannot be spoofed, and it aims to hide "non-content" data, like the sender and receiver of messages, from passive eavesdroppers like those running warrantless wiretapping programs. If Bitmessage is completely new to you, you may wish to start by reading the whitepaper. »

Technitium Bit Chat is a secure, peer-to-peer (p2p), open source instant messenger designed to provide end-to-end encryption. Primary aim of developing this instant messenger is to provide privacy which is achieved using strong cryptography. It can be used over Internet and private LAN networks for instant messaging and file transfer.

Cyanide is Tox client for Sailfish OS .

Echoplexus is an anonymous, web-based, IRC-like chatting platform that makes its best effort to respect your privacy. It allows you to create public or private channels. You can encrypt your chats. You can secure a pseudonym for linkable anonymity. You can code and draw together in real time. You can make free and secure Peer2Peer video and voice calls with the people in your channel using WebRTC.

FireFloo is an instant messaging communicator combining the open XMPP standard (Jabber, GMail Chat etc.) with the echo protocol for multi-encrypted messaging. Use various methods to send chipertext over open standards like libgcrypt and encrypt your private communication.

Toxygen is powerful cross-platform Tox client written in pure Python3.