Skype

Skype screenshots

Send instant messages, share files, and hold video conferences.
Application Settings
Skype 8.1 : Application Settings

Alternative downloads

Whatsapp
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FREE
Send messages, have group chats, and share pictures using the Whatsapp services.
Biba
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Biba provides a rich visual interface for conference calls.
CometChat Messenger
48.0.2564.116
Professional chat application for Mac.