Kopete is described as 'Instant messenger supporting AIM, ICQ, Jabber, Gadu-Gadu, Novell GroupWise Messenger, and more. It is designed to be a flexible and extensible multi-protocol system suitable for personal and enterprise use' and is a popular instant messenger in the social & communications category. There are more than 25 alternatives to Kopete for a variety of platforms, including Linux, Mac, Windows, Android and Web-based apps. The best Kopete 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 Kopete are Conversations, Trillian, Adium and Franz.
Miranda New Generation is a successor of a popular multi-protocol instant messaging client for Windows - Miranda IM . Very light on system resources and extremely fast.
One app for all your messaging.
WhatsApp, Messenger, Telegram, Skype, Zoom, Google Hangouts, Gmail, Slack, Facebook, Facebook Pages, Instagram, Twitter, Outlook, SnapMap, WeChat, LinkedIn, HipChat, and ChatWork.
Germany
EU
Open source Jabber (XMPP) client with multi-account support, clean and simple interface. Being both free (as in freedom!) and ad-free, Xabber is designed to be the best Jabber client for Android .
United States
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.
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.
GermanyEU
qutIM - free open-source multiprotocol ( ICQ, Jabber/GTalk/Ya.Online/LiveJournal.com, Mail.Ru, IRC )
Russia
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.
FranceEU
Conduit is a simple, fast and reliable chat server powered by Matrix. Conduit is an alternative to Synapse and tries to be lightweight and easy to install, but it is still in development.
Chat on the Jabber network (XMPP protocol); focus on features for gateway users The Cheogram Android app allows you to join a worldwide communication network.
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.
Swift is an elegant, secure, adaptable and intuitive XMPP client, with features that make it suitable for a wide range of use scenarios.
United Kingdom
