I know of only two infinitely scalable systems ever built.
One we know, and many people will correctly guess this when asked. It is the internet. The internet started up October 29, 1969 when the first two systems, located in Stanford University and the University of California, connected. Since then, this network has been growing continually:
October 1969: 2
December 1969: 4
December 1971: 23
October 1972: ARPANET went public with a demo linking computers in 40 different locations.