Free
Instantbird
Instantbird: A Versatile Multiprotocol Messenger
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A free program for Mac, by Alexei Kuznetsov.
Echofon for Mac: Streamlined Messaging Experience
Free Instant Messaging App for Mac
Comprehensive Overview of Tweetie for Mac
Nerimity: A Flexible Community Communication Tool
A free app for Mac, by Naan.
Effortless Instagram Uploads from Your Mac
Nambu: A Free Chat App for Mac