🚀 go-pugleaf

In about 1971, I saw a series of pneumatic control gates, flip-flops,
etc. at a french automation installation company.  Each gate was a
machined piece of steel.  There were rows of holes to interconnect the
gates at one end of each gate.  Full circuits were constructed by
stacking up the two inch square by about 1/4 inch thick "wafers"
alternating with gaskets to get the desired function.  Four threaded
bolts were run through the corners and nuts were torqued down to
complete the assembly.  The circuits could be a foot or so high and
were very heavy.  I was told that they were Russian technology and
were useful in explosive atmospheres. 

If memory serves, IEEE spectrum ran a "whatever happened to" article a
couple of years ago describing the technology.