IBM's braindead decision to have 5 (instead of 8)
expansion slots meant
that aftermarket "multifunction" cards became quite popular. MANY of
them advertised SIX functions; after memory, serial, parallel, and
joystick, how many people remember what purported to be the other two
functions?
Real time clock.
I don't recall whether the sixth function was a floppy controller or
a second serial port.