The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- CC-BY-2.0 (2 members)
- CC-BY-NC-ND-2.0 (1 member)
- CC-BY-SA-2.0 (1 member)
- CC-BY-SA-2.5 (5 members)
- CC-by-sa-Bild (1 member)
- CCC (23 members)
- CIA (1 member)
- Cats (2 members)
- Censorship (4 members)
- Chemistry (1 member)
- Christian (4 members)
- Club Der U2-Liebhaber (1 member)
- Codes (43 members)
- Cologne (4 members)
- Comedy (4 members)
- Communications (4 members)
- Computer (452 members)
- Concord (15 members)
- Conspiracy (53 members)
- Conventions (3 members)
- Converter (11 members)
- Copyrighted free use (1 member)
- Corporations (14 members)
- Countries (1 member)
- Cowsay (54 members)
- Crypto (19 members)
- Cybernetics (1 member)
- Cyborg (1 member)
- DIY (7 members)
- Debian (30 members)
- Definitions (172 members)
- Discordian (175 members)
- Discordians (14 members)
- Distributed Computing (6 members)
- Douglas Adams (4 members)
- DrOwl (8 members)
- Drugs (61 members)
- Earth Sciences (1 member)
- Ecology (18 members)
- Economics (2 members)
- Education (4 members)
- Email (10 members)
- Emulation (5 members)
- English (49 members)
- Environment (10 members)
- Esoteric (16 members)
- Events (83 members)
- F5 (2 members)
- Feed (1 member)
- Figlet (34 members)