I always keep a "Idea box" of ideas and concepts about what I can build.

Some of those ideas came to mind when I discovered Nostr:

• A todo list of some kind, public, private or both, maybe gamified.
• A fun virtual room live chat with game like visuals, imagine MMO chats with speech bubbles.
• A game-like client that lets you create and explore other people worlds, imagine a 2d pokemon world with an editor and custom avatars and graphics.
• The idea box itself could be fun to build too, like a brainstorming hub.

Those are fun ideas I'm willing to build, maybe not now and maybe not in Nostr but surely some of those will come true someday.