Pidgin is described as 'Chat program which lets you log into accounts on multiple chat networks simultaneously. This means that you can be chatting with friends on XMPP and sitting in an IRC channel at the same time' and is a leading instant messenger in the social & communications category. There are more than 100 alternatives to Pidgin for a variety of platforms, including Linux, Mac, Windows, Web-based and BSD apps. The best Pidgin alternative is Element. It's not free, so if you're looking for a free alternative, you could try Element or Matrix. Other great apps like Pidgin are Jami, Beeper, SeaMonkey and Element X.
Kaidan is a simple, user-friendly Jabber/XMPP client providing a modern user interface using Kirigami and QtQuick. The back-end of Kaidan is written in C++ using the QXmpp XMPP client library and Qt 5.
Finch is a console-based IM program that lets you sign on to AIM, Jabber, MSN, IRC, Yahoo!, and other IM networks. It runs on Unixes. It uses GLib and ncurses.
Utopia P2P Ecosystem. Utopia is a feature-rich platform that is specifically designed to protect privacy of communication, confidentiality, and security of personal data. Utopia is a decentralized network, with no central server involved in data transmission or storage.
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.
jami-commander (jc for short) is a simple but convenient CLI-based Jami client app for setting up accounts and swarms as well as sending.
Only XMPP, while Pidgin works with multiple systems and protocols.
Ergo (formerly known as Oragono) is a modern IRC server written in Go. Its core design principles are:
qutIM - free open-source multiprotocol ( ICQ, Jabber/GTalk/Ya.Online/LiveJournal.com, Mail.Ru, IRC )
BitlBee brings IM (instant messaging) to IRC clients. It's a great solution for people who have an IRC client running all the time and don't want to run an additional MSN/AIM/whatever client.
Halloy is an open-source IRC client written in Rust, with the Iced GUI library. It aims to provide a simple and fast client for Mac, Windows, and Linux platforms.
Spark is an Open Source, cross-platform IM client optimized for businesses and organizations. It features built-in support for group chat, telephony integration, and strong security. It also offers a great end-user experience with features like in-line spell checking, group chat...
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Modern interface for XMPP communications. Implements OMEMO:2. Works fine.