Digital Equipment Corporation's
enterprise email,
address book,
word processing, and
group calendaring solution of the
late 1980s and
1990s. All-in-1 was a monster to behold. Think about things like
Lotus Notes, or
Novell GroupWise or
Outlook/
Exchange, and then think of it all on a
VT320 green screen or
terminal emulator and you'll have an
idea.
First of all, it was big. You'd need twice the VAX you usually would to run this over standard VMS Mail. It had a complicated message store that attempted to store only one copy of every message on the system at at time, and often worked. Most importantly, it was a hideously complicated piece of code with some big bugs. My school when I was an undergrad used it as the email system. A student sent out a message to all subscribers, and it pummeled the system, and fragments of the message would still show up years later. It was incredible.
In the 1990s, All-In-1 was extended and even had things like IMAP and POP support. Compaq will still maintain it and sell it to you, if you insist, but I certainly can't recommend it.
In some ways, it was ahead of its time.