The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Chronology (5 members)
- City of Fremantle (1 member)
- Clare Davies (1 member)
- Climate change (1 member)
- Clontarf Road (2 members)
- Closeness (1 member)
- Clothing (1 member)
- Cloud storage (2 members)
- Cmd (2 members)
- Co-op (1 member)
- Co-operative (1 member)
- Cockburn (1 member)
- Code (5 members)
- Code projects (1 member)
- Code snippets (1 member)
- Coding (3 members)
- Coding standards (2 members)
- Coffee (5 members)
- Collaboration (5 members)
- Columns (1 member)
- Coming events (11 members)
- Commons (2 members)
- Communication (1 member)
- Community (5 members)
- Compose Key (1 member)
- Composer (1 member)
- Compton MacKenzie (1 member)
- Computers (1 member)
- Configuration (2 members)
- Construction (1 member)
- Control (1 member)
- Controllers (1 member)
- Cookies (1 member)
- Correspondence (1 member)
- Cory Doctorow (1 member)
- Craft (1 member)
- Critical mass (1 member)
- Cross-referencing (1 member)
- Culture (1 member)
- CuppaShack (1 member)
- Cutlery drawer (1 member)
- Cycling (5 members)
- DOS (2 members)
- Daily words (1 member)
- Darkover (1 member)
- Data (7 members)
- DataLog (1 member)
- Data collection (1 member)
- Databases (9 members)
- Date formatting (1 member)