The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Algae (5 members)
- Alternative building (128 members)
- Alternative building design (4 members)
- Alternative energy (1 member)
- Alternative propulsion (3 members)
- Amaranth (12 members)
- Ambiental (8 members)
- America files (33 members)
- America images (0 members)
- AmoSmile (63 members)
- Amsterdam (1 member)
- Anaerobic digestion (34 members)
- Analysis (8 members)
- Anatomy (7 members)
- Andhra Pradesh (2 members)
- Android App Browser Testing (1 member)
- Animal husbandry (13 members)
- Animal power (7 members)
- Animals (31 members)
- Apiculture (4 members)
- Applied Thermodynamics (1 member)
- Appropedia (39 members)
- Appropedia's Public Domain Search (15 members)
- Appropedia, Appropedia Foundation (1 member)
- Appropedia Action Groups (0 members)
- Appropedia Foundation (12 members)
- Appropedia Help (1 member)
- Appropedia WordPress site (1 member)
- Appropedia administration (18 members)
- Appropedia archive (207 members)
- Appropedia books (0 members)
- Appropedia bots (5 members)
- Appropedia collaborations (17 members)
- Appropedia communication (3 members)
- Appropedia communications (6 members)
- Appropedia community (3 members)
- Appropedia content (6 members)
- Appropedia guidelines (8 members)
- Appropedia help (62 members)
- Appropedia internships and volunteering (10 members)
- Appropedia logos (3 members)
- Appropedia maintenance (0 members)
- Appropedia policies (12 members)
- Appropedia policy (0 members)
- Appropedia press releases (0 members)
- Appropedia proposed guidelines (7 members)
- Appropedia proposed policies (18 members)
- Appropedia service learning (7 members)
- Appropedia site development (10 members)
- Appropedia site development archive (31 members)