Fido BBS

Fido BBS is a bulletin board system program for MS/PC-DOS created by Tom Jennings and made available for free use. The FidoNet network was originally built on this software, as it added features to allow Fido BBSs to talk to one another, though other software such as Opus-CBCS was eventually created that was also compatible with this network. Early versions of Opus were designed to be compatible with Fido to the extent that most of their associated files could be preserved across a shift from one of these programs to the other.

Links

 * Wikipedia article on Fidonet
 * FidoNet history - a "long and convoluted document" by Tom Jennings that was written only about a year into that history, but a lot had already happened.