Just like Whatsapp but from your Mac's desktop
Proteus Project
Add fun Snapchat filters to your Mac camera
Unofficial desktop client for Facebook chat
End-to-end encrypted communication
Mattermost
A single program for all your IM accounts
A traditional chat with group videoconferencing
Talk to all of your MSN contact even with your Mac
iOS's iMessage now also on Mac OS
Vector Creations Limited
Ferdi
TSIT
Gajim Developers
Danny
AOL's instant messaging program
64Gram
Chat with friends on this multiplatform messaging client
Multiplatform IM client
Brett Terpstra
Yuuguu Ltd
Chat with your Yahoo and MSN Messenger contacts
An IM combo born of Mozilla and Pidgin
Google
Carlo Gandolfi y Paolo Portalu
Aurelio Jargas
Cooperative whiteboard and voice communication through Jabber
Add a bunch of improvements to iChat
A Multiprotocol Instant Messenger client
Open Source alternative to chat with MSN contacts
A simple Jabber-based IM client
Share files and chat with friends safely