The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Tuggeranong (4 members)
- TwentyTen (2 members)
- Twig (1 member)
- Twitter (1 member)
- Typesetting (2 members)
- Typing (1 member)
- Typography (2 members)
- UNC (1 member)
- URI (1 member)
- URIs (1 member)
- URLs (3 members)
- UTM (1 member)
- UX (1 member)
- Ubuntu (7 members)
- Unesco (1 member)
- Unit testing (1 member)
- Unit tests (1 member)
- University (7 members)
- Updates (1 member)
- Upgrading (1 member)
- Urban (1 member)
- Urban Exploration (1 member)
- Urban resistance (1 member)
- Urbex (2 members)
- Validation (1 member)
- Vall de Núria Rack Railway (1 member)
- Variable sent folder (1 member)
- Variables (1 member)
- Version control (2 members)
- Versioning (1 member)
- Victoria Quay (1 member)
- Victoria and Disraeli (1 member)
- Video (1 member)
- Videos (2 members)
- Views (2 members)
- Visual diary (1 member)
- Volunteering (1 member)
- Voting (1 member)
- W. B. Kimberly (2 members)
- WGV (1 member)
- WKT (1 member)
- Walking (2 members)
- Walking With Water (1 member)
- Walled-gardens (1 member)
- Walter Scott (1 member)
- Watches (1 member)
- Water (2 members)
- Waverley (1 member)
- WeRelate (3 members)
- Web (5 members)