Slidge is a work in progress multi-network puppeteering gateway. This means that contrary to other options an account on the legacy network in question is still required. Currently it supports connecting to Signal, Telegram, Discord, Steam Chat, Mattermost, Facebook Messenger, Skype, and WhatsApp.
This tutorial is a work in progress, please check back later.
Known public instances
There are currently no known public instances of Slidge. Due to the need to store the legacy-network's user credentials on the server it is unlikely that true public instances will be set up. However, your XMPP server admin (which might be yourself) could offer it as a trusted service.
Write your own plugin for Slidge
Slidge is designed to be a framework for gateways and can be easily extended if a library (ideally in python), a CLI client, or a web API for the legacy network exists.