SCO and Xenix let you drive a large number of text terminals or POS systems from a cheap PC. I worked on a factory automation system that had a huge number of serial cables connecting sensors and terminals up to a machine that could barely have run a graphical word processor. It was fantastic, but doomed by open source; you had to pay thousands for extra modules like the C compiler and TCP stack etc, which started to seem a bit absurd by the early 90s. It's a shame their name was later dragged through the mud by people completely unrelated to the original project! There's some good info here: http://www.softpanorama.org/People/Torvalds/Finland_period/x...