MausNet
Mausnet, standing for "Münster Apple User Service" is a Mailbox network similar to FidoNet. It was used mostly in the 1990s in Germany by Atari-Hobbyists. These days it is not used by anyone but a few nostalgic old men yearning for the good ol' days to come back. The users of the network had to use their real name, and doing otherwise was more or less shunned. Messages were sent between 3:00 and 4:00 in the morning, not unlike to FidoNet. MausNet was born out of the frustration with other Mailbox networks, with those being too clunkly and inconvenient to use.
Addresses are formed with the name of the user, the city's license plate abbreviation, and the number of "Maus", or node, so a user with the name Hans Peter from Munich operating the 4th mouse would be "Hans Peter @ MU4" (Back when MausNet was active, the license plate abbreviation would have been "M", so that is not historically authentic of me.) Making money with MausNet is strictly forbidden and shunned as well. According to Wikipedia, there were only 9 mailboxes left in 2011 and the number is shrinking towards 0. There were gateways to the FidoNET, Z-Netz, and Usenet.
A client program for MausNet is called "Maustausch-Programm" a rhyme consisting out of "Maus" being a mouse and "Tausch" being exchange. Such programs existed for nearly every OS of the time, from DOS, Amiga, Atari ST, Window, Linux, OS/2, and Mac.
Trivia
The de-facto logo of Mausnet is the "Puckmaus", a mouse. "Münster" "Münster Apple User Service" stands for the German city of that name, since this is where the origins of that network were.