The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Coding (4 members)
- Coding standards (2 members)
- Coffee (6 members)
- Collaboration (6 members)
- Columns (1 member)
- Coming events (13 members)
- Commons (2 members)
- Communication (2 members)
- Community (7 members)
- Compose Key (1 member)
- Composer (1 member)
- Compton MacKenzie (2 members)
- Computers (1 member)
- Configuration (4 members)
- Construction (1 member)
- Control (2 members)
- Controllers (1 member)
- Cookies (1 member)
- Correspondence (2 members)
- Cory Doctorow (2 members)
- Craft (2 members)
- Critical mass (1 member)
- Cross-referencing (2 members)
- Culture (1 member)
- CuppaShack (2 members)
- Cutlery drawer (1 member)
- Cycling (7 members)
- DOS (2 members)
- Daily words (2 members)
- Darkover (1 member)
- Data (9 members)
- DataLog (1 member)
- Data collection (2 members)
- Databases (11 members)
- Date formatting (1 member)
- Date ranges (2 members)
- Dates (1 member)
- Dave Winer (2 members)
- David Clarke (1 member)
- Debugging (1 member)
- Decoration (2 members)
- Definitions (2 members)
- Deleting (1 member)
- Dependencies (2 members)
- Deployment (1 member)
- Design (9 members)
- Designing (1 member)
- DevOps (1 member)
- Development (3 members)
- Devices (1 member)