I made a little project called pingkey https://pingkey.xyz/ it is a messaging app works like traditional mailing. You setup relays as your mailbox, people write letters and post them to you. Each letter must contain a POW which then turn into a unique POW stamp. It is that simple and I imagine it will become a alternative contact card for those people who are old enough that just hate social network and prefer to keep this simple way just like me. Feel free to try it and contact me https://www.pingkey.xyz/p/ce6232feaec4e6d01a4e00daa3648030c42017bdf589e34b53744fc49c5cba8a and give some feed back. 
Discussion
I have received some letters and collected some pow stamps. thank you! 
Cool!
It would be nice to have it as component, so it can embed it other web pages (I'm thinking about https://oracolo.me).
yes that's part of the plan! Right now you can do something like this in github readme
https://github.com/RetricSu/pingkey
In the future we shall extend that to be a rich embedable component
what about the option to pay instead of doing a POW? If you’re using someone else’s relay, I think they would prefer that.
yeah I have such thoughts too. but there isn't a standard way (NIP) to allow relay charges per-message. Another more interesting thoughts to me is that we can have different stamps that is not comming from POW but human-made. So people can buy the stamp from other people.
I think nostr:npub1h0uj825jgcr9lzxyp37ehasuenq070707pj63je07n8mkcsg3u0qnsrwx8 is working on a whole protocol to make the stamp thing more common
This is really cool. The ux would even be better with an app like #keychat where after the receive keys are generated, there is a add to keychat button or so. Already possible to just copy the key and create a chatid manually but this would even be better. #keychat is really the binding glue for #nostr clients.
That's a good idea 🤙. I will talk to keychat about how to do it.
👍We are adding support for Universal Links.
https://developer.apple.com/documentation/xcode/allowing-apps-and-websites-to-link-to-your-content/
well done, i though about the same app, its a nice idea, very usefull, congrats.
i cant send a message, its says no relays found on the page even though i have the default ones am i missing something? nostr:nprofile1qqsyt3qly8su7u2l5mvu5g9cuqp22axm0w6fa9hw3xp5cek6c4zxk7spr9mhxue69uhhyetvv9ujuumwdae8gtnnda3kjctv9uq3uamnwvaz7tmjv4kxz7fwdehhxarj9emkjun9v3hx2apwdfcz7qg4waehxw309aex2mrp0yhxgctdw4eju6t09utnuyvf
this is great!
might help to make it clear to the sender that the recipient can't "reply" and encourage them to leave contact details if they expect a response
yeah, that's the mode: 1. encourage people to save their key and set up contact info if they expect a response 2. ignore if you don't care responds, eg: maybe you offer a alternative contact way in the message.