A daemon which implements an API bridge to the Signal network. This is for hooking bots into the Signal messaging network as well as connecting other kinds of software and webhooks in.
PushBits is a relay server for push notifications. It enables your services to send notifications via a simple web API, and delivers them to you through various messaging services. For now, only the Matrix protocol is supported, but support for different services like Telegram could be added in the future. I am myself experimenting with Matrix currently because I like the idea of a federated, synchronized but still end-to-end encrypted protocol.
The idea for this software and most parts of the initial source are heavily inspired by Gotify.
Written in Golang.
Apprise allows you to send a notification to almost all of the most popular notification services available to us today such as: Telegram, Pushbullet, Slack, Twitter, etc. One library, many common services and platforms. Comes with a command-line tool, also.
An implementation of Textsecure/Signal in Golang as a CLI tool. Can send and receive one-to-one and group messages.
A web application that sits in front of a command line Signal client that lets you send messages from a web browser. Seems to also have a REST API. Requires a second phone number to set up an account, it's not an extension to an existing Signal setup. Looks like all-Docker-all-the-time but it looks like you can also run it as a system service (a systemd .service file is in the docs, and it says nothing about using Docker for that).
Interestingly, it's a couple of shell scripts.
A tool which interfaces with Signal on behalf of one of your devices to send text messages. Designed for use in scripts. Written in Java, in the AUR, I probably already have it installed on Leandra.
Salut à Toi is a communications framework built on top of XMPP (and all that brings with it) which implements messaging, microblogging, file sharing, e-mail (with a regular mail client), and more. Wherever there is an XMPP server, you can use it. Has multiple front-ends, including a web interface and a desktop client. Written in Python, uses Twisted and Wokkel.