FidoGate
A Unix package that translated between FidoNet and the internet: netmail to email, echomail to Usenet groups, and back again.
FidoNet and the internet coexisted for years without understanding each other's formats. Addresses looked like 2:201/100 on one side and user@host on the other, and echomail packets had nothing in common with Usenet articles. FidoGate, developed by Martin Junius during the 1990s, sat on a Unix box between the two and rewrote headers, addresses and character sets in both directions.
Where the DOS world had UFGATE, FidoGate became the default once nodes started running Linux. It plugged into an ordinary MTA and news server, so an echo could be read in any newsreader. The irony is that it was mostly used in one direction: FidoNet people moving to the internet and wanting to bring their conferences along.