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

Viber Free Messenger and Phone Calls.

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

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

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

WhatsApp Messenger is an instant messaging platform owned by Facebook.

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

ooVoo is a video chat and an instant messaging client.

X-Lite is a freeware VoIP soft phone that uses the Session Initiation Protocol.

SightCall remote support software enables live video streaming and remote access on mobile devices and desktops for customer service and tech support.