The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- JQuery (2 members)
- J K Huysmans (1 member)
- Jane Austen (1 member)
- Jason Scott (1 member)
- Java (2 members)
- John Naughton (1 member)
- Jokes (1 member)
- Joseph Fraser (1 member)
- Joseph Whitworth (1 member)
- Journalism (1 member)
- Joy (1 member)
- Kevin Kelly (1 member)
- Kevin Rudd (1 member)
- Keyboard vs. pen (3 members)
- Kieran Benton (1 member)
- King's Square (1 member)
- Kings Square (1 member)
- Kitchens (1 member)
- Knives (1 member)
- Kobo (5 members)
- Kobo Mini (2 members)
- Kohana (7 members)
- L10n (1 member)
- LOCKSS (1 member)
- LaTeX (2 members)
- Lab notebook (7 members)
- Landscape (1 member)
- Languages (1 member)
- Laptops (3 members)
- Larry Foley (1 member)
- Lawrence Lessig (1 member)
- Leaving Canberra (1 member)
- Leaving the office (1 member)
- Lectures (3 members)
- Legs (1 member)
- Lenovo (2 members)
- Libraries (7 members)
- LibraryThing (2 members)
- Libre (1 member)
- Lighting (1 member)
- Lightweight markup languages (2 members)
- Links (3 members)
- Linux (7 members)
- Linux-voice (0 members)
- Linux/ (0 members)
- Literature (2 members)
- Little Creatures (2 members)
- Living (2 members)
- Local history (1 member)
- Localisation (1 member)