FidoNet
Worldwide message network between BBSes, built in 1984 by Tom Jennings on the observation that long-distance calls are cheaper at night.
The system was a mesh of independent boards that dialled each other on a schedule. During Zone Mail Hour — one hour every night when every node had to be free for traffic — neighbours exchanged bundles of netmail (private letters) and echomail (conference posts), and the packets travelled another hop the following night. A message could take a week to cross the planet and nobody found that strange. Addresses were written 2:201/330 — zone, net, node — and every node appeared in a nodelist distributed weekly. At its 1996 peak there were nearly 40,000 nodes. The internet made the design redundant, but a couple of thousand nodes are still running.