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

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

Ekiga (GnomeMeeting) is a VoIP and video conferencing application for GNOME and Microsoft Windows.

Blink is the best real-time communications client using the SIP protocol.

Viber Free Messenger and Phone Calls.

Empathy is an instant messaging (IM) and voice over IP (VoIP) client which supports text, voice, video, file transfers, and inter-application communication ov…

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