The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Programming (109 members)
- Project Gutenberg (3 members)
- Project Management (1 member)
- Proofreading (3 members)
- Prototyping (1 member)
- Public diary (1 member)
- Publishers (1 member)
- Pubs (2 members)
- Punctuation (2 members)
- QR codes (2 members)
- QRpedia (2 members)
- Quakerism (2 members)
- Queralbs (1 member)
- Queries (1 member)
- Quiet (3 members)
- Quotation marks (1 member)
- Quotations (8 members)
- RMS (1 member)
- RSS (2 members)
- Radio (2 members)
- Rails Through the Bush (1 member)
- Railway (2 members)
- Railways (1 member)
- Rants (1 member)
- ReStructuredText (1 member)
- Reading (54 members)
- Recommendations (1 member)
- Recording (3 members)
- Redaction (1 member)
- Reddit (1 member)
- Redirecting (1 member)
- Releases (1 member)
- Renaming (1 member)
- Renovating (1 member)
- Repositories (1 member)
- Requirements (1 member)
- Requirements analysis (1 member)
- Resurgence Magazine (1 member)
- Reticulation (1 member)
- Reuse (1 member)
- Reviews (1 member)
- Revision control (1 member)
- Revolution (1 member)
- Richard Flanagan (1 member)
- Richard Stallman (1 member)
- Right Ordering (2 members)
- Ripping (1 member)
- Robert Macfarlane (1 member)
- Roel Loopers (1 member)
- Roots (1 member)