Cromemco 4PIO  Board   
This is quite a useful board if you wish to have your computer control power line switches or medical devices.

The Cromemco 4PI0 was an S-100 bus compatible, four isolated I/O port printed circuit board.  The board was designed to operate reliably in high noise industrial control environments where computer system to terminal device electrical isolation was necessary. See the following block diagram.

In  summary, the 4PI0  had the following features:-

Complete  computer system  to terminal device electrical isolation.
Three optically   isolated, 8-bit parallel input  ports.
One input port dedicated to 4PI0  software  status  polling.
Two optically isolated, 8-bit  parallel output  ports.
One magnetic relay isolated, 8-bit parallel output port.
One output port dedicated to software enabling/disabling the  other  three  output  ports.
Optically isolated handshake  lines on all  three input ports;   optically isolated output strobes on the two opto-output ports.
A 5 Kbytes/second  opto-isolated   parallel  data  transfer rate.
Slide  switch  assigned  I/O  port  address  assignments.
Optically  isolated  system RSSET/NMI   (jumper selectable).
  
The manual for the board can be obtained here.