I think this is a pretty niche demand and probably another topic for r/DataHoarder but anyway, here I am.
I created this application to basically have a way to store my WhatsApp messages away from the Google/Meta servers. Or at least not depend so much on Google backup.
Whatsapp has a very limited export functionality, which any user can use through the app’s own interface. Once these messages and media have been exported, you can place them in a folder monitored by ChatVault, send them to an email monitored by ChatVault or upload them via the interface. Once ingested by chatvault, it will record the chat media on disk and save the messages in a database in a structured way. These messages can be accessed in a front end similar to a chat application.
It’s still under development, some things need to be improved (mainly the UI), it’s still far from ideal, it’s true, the way Whatsapp allows us to export messages is quite bad, which makes the entire process of exporting and ingesting it into chatvault quite coupled but it can still be useful for those who want to store their messages independently, just like I wanted.
https://github.com/vitormarcal/chatvault
Edit: add an application interface image
If anyone searches for a comparable alternative for Signal, I can recommend https://github.com/bepaald/signalbackup-tools. You can export a backup in Signal Android and decrypt it and export HTML with that cli. It even offers search via Javascript.