The Amazing World of Software Version Numbers

Harry writes "In theory, software version numbers should be incredibly mundane. In reality, companies have long twisted them for marketing purposes, avoided ones they didn't like, and even replaced them with things other than numbers. I've prepared a tribute to them with some facts and ruminations, but there's a lot I don't know, and I'd appreciate help on the historical side of things. (Anyone know when the standard decimal point-based system came into use?)"