Freemium

Skype is an instant messaging and VOIP (Voice Over Internet Protocol) client to communicate with people in a distant place.

Adium

Open Source

Adium is an Open source multi-protocol instant messaging client for Mac OS X, supports MSN, Jabber, Yahoo! and other networks.

Trillian

Freemium

Trillian is a proprietary multiprotocol instant messaging application.

Jitsi

Open Source

Jitsi (formerly SIP Communicator) is a free and open source multiplatform voice (VoIP), videoconferencing and instant messaging application.

Mattermost

Open Source

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

Franz

Free

Franz is a free messaging app /former emperor of Austria, that combines chat & messaging services into one application.

Rocket.Chat

Open Source

Rocket.Chat free open source chat solution.

qutIM

Open Source

qutIM is free and open-source multiprotocol (ICQ, Jabber, Mail.Ru, IRC, VKontakte) instant messenger.

Zoiper

Freemium

Zoiper is an easy to use sip video softphone, with excellent voice quality and easy to setup.

Telephone

Open Source

Telephone allows you to make phone calls over the Internet or your company’s network.

QuteCom

Open Source

QuteCom (WengoPhone) is a free-software SIP-compliant VoIP client.

Pidgin

Open Source

Pidgin is a free and open-source chat client which supports AIM, Google Talk, ICQ, XMPP protocols.

Tox

Open Source

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

Signal

Open Source

Signal is the most scalable encryption tool.

Linphone

Open Source

Linphone is a free voice over IP (VoIP) service and SIP client.

Kopete

Open Source

Kopete is a multi-protocol, free software instant messaging client released as part of the KDE Software Compilation. Although it can run in numerous environme…

Ring

Open Source

Ring (SFLphone) is an open-source SIP-compatible softphone and instant messenger for Linux, Microsoft Windows, OS X and Android.

Spark

Open Source

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

Psi+

Open Source

Psi is a cross-platform powerful XMPP/Jabber client (Qt, C++) designed for the Jabber power users. Psi+ is a development branch of Psi IM XMPP/Jabber client.