Broadly: https://vaporware.network - we're bringing to market a purely functional Solid State Interpreter (not unlike urbit) VM that employs orthogonal persistence and public key cryptography identity. On top of this stack we are developing a peer-to-peer open source software market (or rather, market of markets, or darknet of markets, if you prefer).
One of the areas we're exploring right now is Nostr integration, starting probably with trivial-to-run, zero-maintenance personal relays. Our stack gets large file hosting for free out of the box, so each user would act as their own sovereign media host (for Nostr notes - or anything else). You'd also be able to trivially serve yourself your own Nostr client UI (a simple method reduce reliance on centralizing - or spying - clients).
Personally though, and more directly to the point at hand: I'm extremely interested in subjective, contextual, non-global, transitive trust and reputation systems. My previous company was working on a prototype of this on urbit, but the concept is even more well-suited for Nostr.
If you'd like to learn more about the urbit version, here was an overview of that project (the general idea is applicable here too): https://gist.github.com/vcavallo/e008ed60968e9b5c08a9650c712f63bd
I'm very happy to discuss either of these with you here or in DMs!