Take in SMS from Twilio as an HTTP GET and pipe it to XMPP, and vice versa.
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 (theoretically) simple set of IP tables rules for building a captive portal on a network.
HTML5 SIP client. Written in Javascript, throw it onto a page and configure it to contact a SIP gateway of some kind. Uses webRTC built into all modern web browsers. Does audio as well as video. Can contact the PSTN if the gateway can.
Github repo: https://github.com/DoubangoTelecom/sipml5