Telegram is a free cloud-based instant messaging platform.

Viber Free Messenger and Phone Calls.

TeamSpeak is software for quality voice communication via the Internet.

Wire is a cross-platform, encrypted instant messaging client created by Wire Swiss. It is available for iOS, Android, Linux, Windows, macOS and Web browser cl…

Bitrix24 is a free (for small businesses) social enterprise platform.

Qiscus provide everything you need to power up your app with chats.

Openfire (Wildfire, Jive Messenger) is an instant messaging (IM) and group chat server that uses XMPP server written in Java.

Tox is a peer-to-peer instant-messaging and video-calling protocol that offers end-to-end encryption.

Signal is the most scalable encryption tool.

Mattermost is an open source, private cloud Slack-alternative, Workplace messaging for web, PCs and phones. MIT-licensed.

Gajim is an instant messaging client for the XMPP protocol which uses the GTK+ toolkit.

Apache Spark is an open-source cluster-computing framework.

Zulip is a chat and collaborative software.