@action_jay that's something I'm asking myself.
I use [kanka](https://kanka.io/) for my worldbuilding stuff because it's self-hostable.
I planned to move everything to [otterwiki](https://otterwiki.com/) one day maybe...
For the virtual tabletop stuff.. I found [mythic table](https://gitlab.com/mythicteam/mythictable/). #FoundryVTT is self-hostable but not #opensource.