I am wondering if there is a chat program that works locally when the internet is out but still be connected to from the internet. I know this will be something that is self hosted.
Bonus points if I can set it up on the raspberry pi that is running Home Assistant.
I have used Rocket.Chat before, their free version supports most of the features they have, and the web client is good. You can setup webhooks in and out for different automations you may want.