A video game app. Library of games. Shows top10 scores for each game. Multiplayer a must! Nostrcade? based loosely on https://www.fightcade.com :D

Another idea might be something in the VR/AR/MR arena which lets you surf the nostrverse and just visit events and relays in new ways. Or VR worlds in Nostr, over VR-Centric relays. Something like VRChat done exclusively over Nostr would blow my mind away. Foundation for the real metaverse (not that crap zuck stole from stephenson)