Lockbox would be my personal favorite in a slightly-better functioning nostr world. It might even be my favorite as is.

Helping to create the feed for wss://relays.land/spatianostra has been super cool. The staging area is interesting to browse all on it's own. That dynamic voting system has huge potential in the curation space. I can, have, and will rattle on about that anytime.

I really like wss://cellar.nostr.wine too. Not that I have much to say that will retain future relevance, but it's really cool to watch my notes be searched out & imported on command.

Really, any of these concepts that bring relays out of the shadows & and radically change the nostr experience are awesome to me. Zapbox, creatr, utxo's algorelay, my own quiet space with relaytools... I'm sure there are others but I'm kind of tired. So much more is possible than spam protection.