Rails and the books were both byproducts of 37 Signals (ie stuff they were doing anyway, so they released it to the public - not that that is cost-free, but it'

Rails and the books were both byproducts of 37 Signals (ie stuff they were doing anyway, so they released it to the public - not that that is cost-free, but it's not as intensive as doing it from scratch). And cars are his hobby.