Some take issue with calling Red Hat the first billion-dollar open source company. As Linux kernel maintainer Greg Kroah-Hartman notes, Google, Facebook, and Amazon were built on open source software, and IBM made billions off of Linux. "There are lots of companies that rely entirely on open source software, and give back in various ways to the communities involved," he said. "Loads of them are above the billion-dollar mark." (http://arstechnica.com/business/news/2012/02/how-red-hat-killed-its-core-productand-became-a-billion-dollar-business.ars/2)