Every app built to use lightning like Fountain or say Geyser is a layer three app. Nostr apps are layer three apps.
Discussion
No, they are layer 2 apps
& nostr is an entirely separate thing from bitcoin
Depends on your strict definition of "layer" which in my thinking is fluid and based on perspective. Each of the apps that Jack mentions have internal "networks" to their ecosystem, thus a strong argument for layer 3. They are the third layer of value away from BTC layer 1.
No definitely not.