The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Tabular (2 members)
- Tabulate (8 members)
- Tasks (1 member)
- Taxonomy (1 member)
- Tea shelf (2 members)
- Technique (1 member)
- Technology (30 members)
- Telecottage (1 member)
- Telework (1 member)
- Templates (3 members)
- Temporal reasoning (2 members)
- Tenuous literary references (1 member)
- Terminology (1 member)
- Testing (2 members)
- Text (1 member)
- The Attic (1 member)
- The Co-operative Food Shop (2 members)
- The Day We Fight Back (1 member)
- The European (2 members)
- The Guardian (3 members)
- The Mystery of Edwin Drood (2 members)
- The Queen (1 member)
- The Thin Blue Line (1 member)
- The Unknown Craftsman (1 member)
- Themes (3 members)
- Theo Aronson (1 member)
- Theo Coulthard (1 member)
- Things (7 members)
- ThinkPad (2 members)
- Thomas the Tank Engine (1 member)
- Thunderbird (1 member)
- Tim Berners-Lee (1 member)
- Tim Brook-Taylor (1 member)
- Time (2 members)
- Timekeeping (2 members)
- Tom Bihn (2 members)
- Tom M. Wilson (1 member)
- Tools (7 members)
- Topics (1 member)
- Torrents (1 member)
- Trains (4 members)
- Transport (18 members)
- Travelling (4 members)
- Travels with Charley (2 members)
- Treenails (2 members)
- Trees (4 members)
- Trello (1 member)
- Tropicana (1 member)
- Trove (1 member)
- Truth to Materials (2 members)