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