People can drop Actors or spells in FVTT from their world into a compendium, then they’d have access to it from other worlds so they can share their stuff between worlds.
One issue though is that in FVTT, when you ‘create compendium’, that becomes a world compendium that isn’t accessible to other worlds, so you would need to use a module compendium since modules are shared between all world. One issue with that is that if the module is updated, the compendium gets overwritten to the new version (I’ve seem someone spend hours filling up their dnd5e system’s compendium with the full monster manual only to have it wiped and reset to the SRD when they updated the system).
One way to avoid that problem is to create a module of your own, which would therefore never be updated and only drop stuff into the compendiums of that module.
Plan here is to add to the Table Tools a “Create Shared Compendium” option that would let user name the module and have it generate a new module for them with all the compendiums they may need pre-configured.
Also wondering if I shouldn’t force compendiums from modules/systems to be read-only, but it doesn’t look like NeDB supports opening read-only db files.