The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Cave game tech test (6 members)
- Cellular organisms (1 member)
- Cereal-based food (1 member)
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- Classification (1 member)
- Classification systems (0 members)
- CommonsRoot (1 member)
- Commons templates-en (15 members)
- Commons templates-i18n (2 members)
- Commons utility templates (1 member)
- Companies based in Kyoto (1 member)
- Companies by name (1 member)
- Companies listed on NASDAQ (1 member)
- Companies listed on the Frankfurt Stock Exchange (1 member)
- Companies listed on the Tokyo Stock Exchange (1 member)
- Compiz (1 member)
- Computer hardware (1 member)
- Computing (1 member)
- Concepts (0 members)
- Concepts in metaphysics (2 members)
- Concepts in physics (1 member)
- Conceptual distinctions (1 member)
- Conceptual systems (1 member)
- Created with:I18nTemplates (1 member)
- Created with ... I18nTemplates (1 member)
- Created with Inkscape-undef (1 member)
- Cross-platform software (2 members)
- Cubes in pixel art (1 member)
- Cubic objects (1 member)
- Custom license tags (1 member)
- Cyclic group C3 (1 member)
- Cyclic group C6 (1 member)
- Deities and spirits (2 members)
- Deltarune (1 member)
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- Deprecated templates (1 member)
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- Dimensions (1 member)
- Dog breeds by name (1 member)
- Domains (biology) (1 member)
- Electronics manufacturers of Japan (1 member)
- Energy technology (1 member)
- Entities (1 member)
- Eukaryota (0 members)
- Eutheria (1 member)
- Extant Miocene first appearances (1 member)
- Extant Neogene first appearances (1 member)
- Fifth-generation video game consoles (1 member)
- File emblems (1 member)