I have my own Matrix & Bridges setup (just like Beeper but with too much maintenance). It's super easy to write bots that you can then hook into Signal, WhatsApp etc, because essentially you only need to talk to your Matrix server, and the bridges take care of the rest. Talking to Matrix is easy - there's a straightforward HTTP API.
Any docs for hooking up a bot to WhatsApp? I have WhatsApp bridge running successfully and a python echo bot running that I can call in a Matrix room, but I can't invite the bot to a WhatsApp room, it says User is already in the space
The other day I connected the matrix-chatgpt-bot (https://github.com/matrixgpt/matrix-chatgpt-bot) with WhatsApp - it was very funny to see how people reacted.