Adium is described as 'Free and open source instant messaging application for Mac OS X, written using Mac OS Xs Cocoa API, released under the GNU GPL and developed by the Adium team. Based on the libpurple protocol library, Adium can connect you to any number of messaging accounts on any' and is a very popular instant messenger in the social & communications category. There are more than 50 alternatives to Adium for a variety of platforms, including Linux, Mac, Windows, Android and BSD apps. The best Adium alternative is Element. It's not free, so if you're looking for a free alternative, you could try Element or Pidgin. Other great apps like Adium are Element X, HexChat, Trillian and Messenger.
Bitmessage is a P2P communications protocol used to send encrypted messages to another person or to many subscribers. It is decentralized and trustless, meaning that you need-not inherently trust any entities like root certificate authorities.
Instantbird is an instant messaging client based on Mozilla XULRunner and the open source library libpurple created by the software developers of Pidgin . Over 250 add-ons allow user customization of, and addition of, features.
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QQ is a widely used Chinese instant messaging service developed by Tencent, offering chat, voice, and video communication. It integrates social networking features like groups, forums, and customizable avatars to enhance user interaction.
China
KakaoTalk is a phone number based messenger service that allows users anywhere in the world to chat one-to-one or in a group for free. (no SMS service)
South Korea
BeagleIM is a lightweight and powerful XMPP client developed by Tigase, Inc. It provides an easy way to start using the XMPP Protocol (formerly known as Jabber) if you've never used it before. Veterans of the protocol will find many features here they are familiar.
United States
Zoho Cliq simplifies your team communication with organized conversations, information that's easy to find and by connecting to the tools you love. Transform ideas into reality with your team. With channels, your team communication is visible, transparent and efficient.
India
qutIM - free open-source multiprotocol ( ICQ, Jabber/GTalk/Ya.Online/LiveJournal.com, Mail.Ru, IRC )
Russia
Brosix is a secure communication tool for businesses that need a functional way to organize their internal communication.
United States
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Kadu is an open source Jabber/XMPP and Gadu-Gadu instant messenger client for Linux, *BSD, Mac and Windows.
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