You can categorize most GNU/Linux distributions as either community or commercial. Community-based distributions like Debian, Fedora, or CentOS are maintained largely by volunteers and donations of services or money, while commercial distributions like Suse, Red Hat, or Xandros are backed by a company and compete directly against proprietary operating systems such as Windows and OS X.
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Now, the two categories are harder to tell apart. Several companies are involved with both commercial and community distributions — for instance, Novell is involved with both Suse Linux Enterprise and openSUSE, and Red Hat with Red Hat Enterprise Linux and Fedora. In these cases, the two distros are technically separate, but business interests may spill over into the community distribution from time to time. Not only does Red Hat employ several Fedora community leaders, but, in its security crisis a couple of months ago, Red Hat seems to have made decisions that affected Fedora without consulting its board.