How to unite Internet clients who do not know each other?

Question

Computer networks

In general, suppose that there are applications, for example, chat and, for example, on a smartphone, how can clients find each other without a server? There is a file in the bit-torrent protocol that stores the address of the first source ...

Answer 1

Google “decentralized messengers”, but keep in mind that it works slowly and poorly and has not yet been invented better than a link server.

Answer 2

Through the Internet - without intermediaries in any way (our own or others), and auto-detection is possible in the local area.