Maybe Notion? Notion based blog nostr comments
What existing apps could have a Nostr integration or plugin?
Stuff like https://obsidian.md/, https://fraidyc.at/ or https://github.com/AntennaPod/AntennaPod.
Discussion
I've looked at this now. The simplest idea would be to do like Obsidian and allow people to write articles on Notion and publish them to Nostr, their "integration" stuff doesn't allow anything very useful, it's just a very limited HTTP API, there is no "push" model or any way to augment the Notion UI or call an integration from the inside.