The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Minion (1 member)
- Miscellaneous (88 members)
- Mocca Lounge (2 members)
- Modernity (1 member)
- Modules (2 members)
- Monitors (2 members)
- Montreal (2 members)
- MoonMoon (1 member)
- Mortise and tenon joints (1 member)
- Morton codes (1 member)
- Mountain Designs (1 member)
- Movies (1 member)
- Moving (1 member)
- Mtools (1 member)
- Museum of Perth (1 member)
- Music (1 member)
- MySQL (6 members)
- NaBloPoMo (4 members)
- Namespaces (1 member)
- National Library of Australia (1 member)
- Nature (3 members)
- Neal Stephenson (2 members)
- Necromancy (2 members)
- News (4 members)
- Newspapers (2 members)
- Nikon D60 (1 member)
- Ninthfloor.org (1 member)
- Nomenclature (2 members)
- Non-fiction (4 members)
- Noongarpedia (1 member)
- Not good enough (2 members)
- Notes (1 member)
- Nyunga (1 member)
- O'Connor Community Garden (1 member)
- OCD (2 members)
- ODK (2 members)
- ORM (2 members)
- Off the Map (1 member)
- Offsite (0 members)
- One thing well (2 members)
- Ontology (5 members)
- OpenLibrary (2 members)
- OpenRosa (2 members)
- OpenStreetMap (8 members)
- Open Data Kit (2 members)
- Open Source (4 members)
- Open content (69 members)
- Open source (2 members)
- Open standards (1 member)
- Optimism (2 members)