The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Tuggeranong (4 members)
- TwentyTen (3 members)
- Twig (2 members)
- Twitter (2 members)
- Typesetting (4 members)
- Typing (1 member)
- Typography (2 members)
- UNC (1 member)
- URI (1 member)
- URIs (2 members)
- URLs (4 members)
- UTM (1 member)
- UX (1 member)
- Ubuntu (10 members)
- Unesco (1 member)
- Unit testing (1 member)
- Unit tests (1 member)
- University (9 members)
- Updates (2 members)
- Upgrading (1 member)
- Urban (1 member)
- Urban Exploration (1 member)
- Urban resistance (2 members)
- Urbex (2 members)
- Validation (2 members)
- Vall de Núria Rack Railway (1 member)
- Variable sent folder (2 members)
- Variables (1 member)
- Version control (2 members)
- Versioning (2 members)
- Victoria Quay (2 members)
- Victoria and Disraeli (1 member)
- Video (1 member)
- Videos (3 members)
- Views (2 members)
- Visual diary (2 members)
- Volunteering (1 member)
- Voting (2 members)
- W. B. Kimberly (2 members)
- WGV (1 member)
- WKT (2 members)
- Walking (3 members)
- Walking With Water (2 members)
- Walled-gardens (1 member)
- Walter Scott (2 members)
- Watches (2 members)
- Water (2 members)
- Waverley (2 members)
- WeRelate (3 members)
- Web (7 members)