Open Source Communication Software
Simple Machines Forum
Simple Machines Forum or SMF in short is a free and open-source forum software. SMF can be used to build your own online community that you self-host on a host of your choice. Simple Machines Forum comes packed with features for customization, extension and management of your community. The template engine puts you in control of the design of your community. The plugin architecture makes it easy to extend and provide further feautres though third-party built packages.
Flarum
A free and open-source modern forum software written in PHP. With Flarum you can eaisly setup your own discussion froum and host it online.
Signal
Signal is a cross-platform encrypted messaging application that has a strong focus on privacy. The application is developed by Signal Messenger LLC and provides users with features like one-to-one and group messages, which can include files, voice notes, images and videos. The software is famous for being used by the whistleblower and privacy advocate Edward Snowden who once said "I use Signal every day, it is the most scalable encryption tool we have".
LayerBB
LayerBB is a small yet feature rich, free and open-source community software written in PHP. LayerBB enables you to quickly and easily start your own community while providing great flexibility and customisability.
KDE Connect
KDE Connect is an open source software that enables communication between all your devices. With KDE Connect, you can get all your phone notifications instantly synced to your desktop, so that you never miss that critical message. You can also directly reply to text messages from the computer without having to pick up your mobile device. If you want to share files or links between devices, KDE Connect got you covered as well. As the software allow you to browse and share your phone files remotely or quickly open a link on the other device.
GNU social
GNU social connects you to a free network of thousands of communities that discuss daily on a variety of topics, each being part of the whole. GNU social supports both single-user and community modes and can be used in an intranet environment or as part of the wider open network. The free and open source microblogging server is written in PHP and built on-top of the OStatus standard for inter-operation between installations.
Subsocial
An open platform for decentralized social networks and marketplaces. It's censorship-resistant and has built-in monetization methods. Built with Polkadot and IPFS tech stack.
reddit
Reddit is a social news aggregation network and community. On reddit people can share and discuss web content in user created communities called subreddits. Each subreddit rally around specific topics where only related content can be shared, and rated. The web content that can be shared or reddit includes links, text posts, and images which can all be upvoted or downvoted.
Irssi
Irssi is a terminal based IRC client for UNIX-based operating systems. Irssi comes with IRC built-in and is multi-protocol friendly for module authors, it also support integration with SILC and ICB protocols via plugins. The application easily integrates with your window manager, your terminal emulator, your remote connection, your terminal multiplexer, your IRC bouncer and your IRC adapter. Allowing you to use Irssi virtually everywher throughout your system. Irssi is free software licensed under the GPLv2, available for macOS, Linux, BSD, Solaris, and Cygwin.