The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Planing (3 members)
- Planning (2 members)
- Plugin (2 members)
- Plugins (12 members)
- Podcasts (3 members)
- Point Counter Point (2 members)
- Politics (5 members)
- Popups (1 member)
- Porting (1 member)
- Portraits (1 member)
- Posts written when drunk (4 members)
- Preservation (3 members)
- Printable WeRelate (4 members)
- Printing (1 member)
- Priorities (1 member)
- Production (1 member)
- Programming (115 members)
- Project Gutenberg (5 members)
- Project Management (2 members)
- Proofreading (4 members)
- Prototyping (2 members)
- Public diary (1 member)
- Publishers (1 member)
- Pubs (2 members)
- Punctuation (4 members)
- QR codes (2 members)
- QRpedia (2 members)
- Quakerism (3 members)
- Queralbs (1 member)
- Queries (2 members)
- Quiet (4 members)
- Quotation marks (2 members)
- Quotations (11 members)
- RMS (1 member)
- RSS (4 members)
- Radio (3 members)
- Rails Through the Bush (1 member)
- Railway (3 members)
- Railways (2 members)
- Rants (1 member)
- ReStructuredText (2 members)
- Reading (59 members)
- Recommendations (1 member)
- Recording (3 members)
- Redaction (1 member)
- Reddit (2 members)
- Redirecting (1 member)
- Releases (2 members)
- Renaming (1 member)
- Renovating (2 members)