Xabber is described as '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' and is a popular instant messenger in the social & communications category. There are more than 100 alternatives to Xabber for a variety of platforms, including Android, iPhone, Windows, Mac and Linux apps. The best Xabber alternative is Signal, which is both free and Open Source. Other great apps like Xabber are Telegram, Element, Matrix and Pidgin.
It is the brand new, and fastest ever, Matrix client. It is for personal and community use, and will support enterprise functionality later this year.
Encrypted messenger supporting multi-platform access, unlimited group and private chats, file and voice message sharing, decentralized operation, open-source code, custom themes including dark mode, advanced moderation, push notifications, and no advertisements.
Offers secure messaging with end-to-end encryption, unlimited free calls, group chats for up to 250 members, rich media sharing, emoji reactions, AR lenses, self-destruct messages, affordable international calls, community channels, and robust privacy across devices.
Conversations is a privacy focused, open source XMPP Texting [Jabber] client for Android 4.0+ smart phones with wife-approved easy encryption [OTR, OMEMO, or GPG].
Linphone is one of the most famous open source softphones in the world. It is fully SIP-based, for all calling, presence and IM features.
Trillian is an instant messaging app that works on phones, tablets, and desktops while keeping your chats neatly synchronized between all of them! We think conversation should be easily shared between all of your devices, not trapped as text messages on your phone.
Provides comprehensive communication features including group video calls, voice calls, fast messaging, photo sharing, and location mapping. Access through mobile and web platforms with real-time notifications, ensuring seamless interactions using multimedia tools.
Feature-rich XMPP client for advanced users offering strong customization options, secure encrypted messaging (TLS, OpenPGP, OTR, OMEMO), file transfers, audio/video calls, support for animated emoticons, modern themes, group messaging, and multi-platform compatibility.
An alternative Telegram client based on TDLib, with higher speed, slicker animations and experimental features.
Empathy is a messaging program which supports text, voice, video chat, and file transfers over many different protocols. You can tell it about your accounts on all those services and do all your chatting within one application.
ChatSecure is a free and open source messaging app that features OTR encryption over XMPP. You can connect to your existing accounts on Facebook or Google, create new accounts on public XMPP servers(including via Tor), or even connect to your own server for extra security.
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It can do more or less the same, and it's also very similar in concept and design (free software also).