This article at Linuxforums covers the ten largest Linux distributions – amongst them are Debian, Ubuntu, Knoppix and Mepis.
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Debian is one of the oldest GNU/Linux distributions. It was created in 1993 by Ian Murdock who named it after the combination of his own name and the one of his then-girlfriend (now wife) Debra. The Debian project is non-commercial and gathers more than a thousand developers throughout the world.