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.
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