Meshtastic is a great one. People are making all kinds of software for it. I saw someone developing a BBS for it. For those who want a summary: Meshtastic is a very low bandwidth radio system for creating mesh networks. The speed of data transfer is similar to the modems of the 80s, so you aren’t transferring anything but text. But the range is good and the hardware is cheap, and it is completely stand alone. It can normally pair with something like a phone for ease of access, but has its own dedicated device for a radio.
I’ve been using and reasonably satisfied with A.R.M. https://github.com/automatic-ripping-machine/automatic-ripping-machine
It uses MakeMKV and Handbrake, but streamlines the whole process.