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you had me until the last sentence.
can you share an example of any system that incurs no running costs?
Yes, Keet, and other apps that will be built on the recently released Pear runtime.
Keet runs on zero infrastructure. No servers and no relays (unlike Nostr). The only thing that the developers have done to get the P2P network up and going is to run a few instances themselves, and it's from specially signed instances (again, not servers) that updates to the software are propagated.
The Bitcoin chat room on Keet currently has over 1400 members and the chat is 'hosted' or shared across those members devices (mainly phones and some desktops). No servers, no running costs.