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