Open-source Viber alternatives

Telegram Desktop is the official desktop client for the Telegram messaging service. The repository holds the complete source code and build instructions for an app built on the Telegram API and the MTProto secure protocol. It is written in C++, and the license is GPLv3 with an OpenSSL exception.

Builds are published for 64-bit and 32-bit Windows 7 and above, including portable versions, for macOS 10.13 and above, and for Linux as a static 64-bit build, a Snap and a Flatpak. Older systems are served by version 4.9.9, the last release that supports macOS 10.12 and older Linux with glibc. The client connects to Telegram's hosted service rather than a server you run yourself, so using it means having a Telegram account.

This repository holds the official source code for the Telegram messaging app on Android. Telegram describes itself as a messenger focused on speed and security that is free to use. The code is written in Java and published under the GPL-2.0 license, alongside compilation instructions for developers.

Developers are invited to use Telegram's API and this code to make their own applications, subject to conditions: obtain your own API id, avoid using the Telegram name or standard logo, follow the security guidelines, and publish your code to comply with the licenses. The build supports reproducible builds with dummy keystore and Firebase files that must be replaced before releasing your own APKs. Compiling needs Android Studio, the Android NDK and SDK, and cloning with submodules. Protocol documentation is available for the Telegram API and MTProto.

Signal Android is the source code of the Signal private messenger for Android. Signal describes itself as a simple and secure messenger that sends messages and places voice and video calls over WiFi or a mobile data connection, with privacy protections always switched on. The app is written in Kotlin and released under the AGPL-3.0 license, and it is free to use.

The app is available from the Play Store and signal.org, with versions for iOS and desktop as well. The repository explains how to report bugs on GitHub, join the beta channel on Google Play, contribute translations through the community forum, and submit code. New contributors are encouraged to start with small bug fixes, and larger ideas should be discussed on the community forum first. The client depends on Signal's own hosted service, so there is no self-hosted server option here.

SimpleX is a messaging network built around the idea that it should not assign identifiers of any kind to its users, not even random IDs, which the project says makes it private by design. The goal is to protect not just message content but also metadata, meaning who talks to whom and when.

Messages use double-ratchet end-to-end encryption with an additional encryption layer. Apps are available for Android and iOS, with an iOS TestFlight preview that gets new features a week or two earlier but is limited in the number of users, and a terminal client runs on Linux, macOS and Windows. The README invites readers to install the app, connect to the team and user groups, make a private connection with a friend, help with translations and donate. The core is written in Haskell.

SimpleX Chat is licensed under AGPL-3.0, and its protocol and server software are open so that others can host relays. It is aimed at people who need stronger privacy guarantees than mainstream messengers provide, such as journalists, activists and privacy-conscious individuals.

Signal Desktop is the desktop version of the Signal private messenger for Windows, macOS and Linux. It links to the Signal app on an Android or iOS phone, which lets you send and read messages from your computer. It is written in TypeScript and released under the AGPL-3.0 license.

Both a production version and a beta version can be installed. Support is provided through a support site with answers to common questions and a community forum, which is also where feature requests and questions go, while bugs are reported as GitHub issues. Contributions are welcome, including non-code ones, and the repository has a contributing guide.

Signal is run by an independent 501(c)(3) nonprofit, the Signal Technology Foundation, and donations can be made from inside the apps or on the web. The repository includes a cryptography notice explaining that the software contains encryption and may be subject to import, possession and export rules in some countries.

Element Web is a client for Matrix, the open protocol for decentralized messaging. It is the web and desktop application formerly known as Vector and Riot, and it lets people join rooms, chat in teams and communities, and collaborate across Matrix servers rather than inside a single vendor's network.

The client is built with TypeScript on top of the Matrix JS SDK. The README defines support tiers for browsers, covering recent versions of Chrome, Firefox, Edge and Safari on desktop, best-effort handling for ESR and extended-stable releases, and community support for mobile web. For phones and tablets the maintainers recommend the native Element X apps for Android and iOS.

It is released under the AGPL-3.0 license and is typically served from your own web host or used through the hosted app from the vendor, Element. Related products such as Element Call and the Enterprise Server Suite are mentioned as part of the wider Element offering. Changes are tracked on GitHub with regular release cycles.

Signal iOS is the iPhone and iPad client of Signal, a free and open-source messaging app made for simple, private communication with friends. The same service is also available on Android and as a desktop application, so conversations are not tied to a single platform.

The app is written in Swift. The maintainers state that it collects no analytics or telemetry, which is why they rely on bug reports sent through the Support Center to troubleshoot problems. Developers can follow BUILDING.md to set up a build environment and read the contribution guidelines, while ideas and discussion go through the community forum run for Signal Foundation projects.

The repository is released under the AGPL-3.0 license. Because the software includes cryptographic functionality, the README carries a cryptography notice reminding users to check their country's rules on encryption software and documents its export classification. Signal itself operates as a hosted messaging service rather than something you run on your own server.

FluffyChat is a nonprofit, open-source client for the Matrix network, written in Flutter. Its goal is to be an easy-to-use instant messenger that is open source and accessible to everyone. Because it speaks the Matrix protocol, it works with Matrix accounts and servers rather than a proprietary service of its own.

Users can send all kinds of messages, images and files, record voice messages, share locations and take part in video calls with Matrix RTC. It supports push notifications, unlimited private and public group chats, public channels, spaces, custom emotes and stickers, and moderation tools covering the Matrix feature set. Privacy features include end-to-end encryption, encrypted chat backup, emoji verification and cross-signing, and it follows Material You design.

For organizations, configuration can be pushed to Android and iOS devices through mobile device management since version 2.10.0, and on the web through a config.json file. Building from source requires Flutter and Rust. It is licensed under AGPL-3.0, with translations handled through Weblate and installation instructions on the project website.

Delta Chat Desktop is the desktop application for Delta Chat, described as a decentralized private messenger with chat-shared tools and games. Project topics show that it works over standard email protocols, IMAP and SMTP, and supports Autocrypt-based end-to-end encryption, so conversations can run over existing email accounts instead of a single central service.

The default edition is built on Electron and is the version deployed in app stores and used by most people. A highly experimental browser edition with a web server component is meant only for developers and automated testing, and a work-in-progress edition based on Tauri lives in a separate repository. The code is written in TypeScript and licensed under GPL-3.0.

Binary releases are published for supported platforms, with Flatpak and Arch Linux options on Linux, Homebrew or a DMG on macOS and installers for Windows. User documentation covers troubleshooting, command-line flags, keybindings and creating custom themes, while developer documentation explains logging, styling, updating the core, end-to-end tests and the release process.

Session Desktop is the desktop application for Session, a private messenger that is decentralized and uses onion routing. It connects to Oxen Service Nodes, a set of distributed, Sybil-resistant servers. Some of these nodes store messages while a recipient is offline, and others provide onion routing that hides users' IP addresses.

Releases are signed, and the README walks through verifying them by checking a GPG signature on the published hashes and then comparing the hash of the downloaded file. The project also lists supported platforms and system requirements, accepts pull requests on a development branch, and invites volunteers to help with translations. Build instructions are in the contributing guide.

The client is written in TypeScript and licensed under GPL-3.0. It is distributed from getsession.org and maintained under the Session Foundation. The README points to the Session whitepaper for a full explanation of how the system works.