Nostr with NIP13 https://github.com/nostr-protocol/nips/blob/master/13.md defines a way to generate proof of work (a la bitcoin) on the client side.
A relay and a client can filter event based on the difficulty.
Nostril is a command line tool that let you produce a message with proof of work.
Here an example.
https://nostr.rocks/event/00000566c20b887f766c29941b38d87f1d02e5073b5b5e4310dc5648ffd0be32
https://s3-eu-west-1.amazonaws.com/public-bucket-john-897867457987890896/1660723767003.jpg
What about proof of rhyme?
You have to rap every time
If not, your message isn't fine
Remember: two plus six isn't nine
The concept is very similar to this one which is really cool
Wahou never heard of that project. Like the idea
Even if all messaging systems worked with PoW antispam.
Bitcoin would still be considered boiling the oceans.
Only by irrelevant people