Instant Messaging
Adium
A Multiprotocol Instant Messenger client
AIM for Mac
AOL's instant messaging program
aMSN
Open Source alternative to chat with MSN contacts
Camfrog
A traditional chat with group videoconferencing
Chax
Add a bunch of improvements to iChat
Coccinella
Cooperative whiteboard and voice communication through Jabber
Franz
A single program for all your IM accounts
Instantbird
An IM combo born of Mozilla and Pidgin
Messages
iOS's iMessage now also on Mac OS
Messenger for Desktop
Unofficial desktop client for Facebook chat
Microsoft Messenger
Talk to all of your MSN contact even with your Mac
Nimbuzz!
Chat with friends on this multiplatform messaging client
Palringo
Multiplatform IM client
Retroshare
Share files and chat with friends safely
Yahoo Messenger for Mac
Chat with your Yahoo and MSN Messenger contacts
