FidoNet
A worldwide hobbyist network of personal computers which exchanges e-mail, discussion groups, and files. Founded in 1984 and originally consisting only of IBM PCs and compatibles, FidoNet now includes such diverse machines as Apple IIs, Ataris, Amigas, and Unix systems. Though it is much younger than Usenet, FidoNet is already (in early 1991) a significant fraction of Usenet's size at some 8000 systems.
[The Jargon File]