Skype

Skype screenshots

Send instant messages, share files, and hold video conferences.
Preferences
Skype 6.6 : Preferences

Alternative downloads

Whatsapp
0.3.4480
FREE
Send messages, have group chats, and share pictures using the Whatsapp services.
Biba
3.14.3972
Biba provides a rich visual interface for conference calls.
CometChat Messenger
48.0.2564.116
Professional chat application for Mac.