I've got kinda sidetracked here waffling on about the history of dial-up BBS systems. What I really want to be concerned with is what made The Microsoft Network unique and interesting: the interface.
The big thing in Windows 95 was their new shell. They wanted everything to go through this. They had this vision of every object in the computer being represented as a shell object, so there would be a seamless intermix between files, documents, system components, you name it. They had this project called Cairo that was supposed to throw out that scruffy old file-based filesystem and bring in a shiny new Object Based File System instead. It never happened, so we'll never know exactly how it might have turned out. But the brave lads at MS didn't give up that easily and so the idea stayed on, admittedly without the tech to back it up, and the principles wormed their way into such glorious developments as The Microsoft Network.
And so The Microsoft Network wasn't a program you loaded like CompuServe. It was part of the OS, with folder icons that looked just like real folders. It was a kind of version of the Web where you could browse online data the same way you browsed your file system. This is what made it cool.
I vaguely remember something about this project - and of course, the whole concept of integrating literally everything into the Windows 95 shell did see some adoption here and there in the early days of Windows 95. Looking at it from today's perspective, I still kind of like it - Microsoft would try the concept again with Windows Phone 7, where services like Twitter and Facebook were supposed to be integrated into the operating system, without having to use crappy applications to access them.
That is still a good idea today.