FTN = Fido (or fidostyle, depending on who you ask) Technology Network, aka echomail. It works basically by front-end mailers dialing each other up and exchanging packets of compressed messages, allowing bbses to network together their message bases. The biggest and most famous FTN is Fidonet, but there have been literally hundreds of them, from small ones like tabnet to big honking ones like cybercrime international. Contains simple routing capabilities.