The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Algae (6 members)
- Alternative building (146 members)
- Alternative building design (4 members)
- Alternative energy (1 member)
- Alternative propulsion (2 members)
- Amaranth (11 members)
- Ambiental (8 members)
- America files (33 members)
- America images (0 members)
- AmoSmile (74 members)
- Amsterdam (1 member)
- Anaerobic digestion (37 members)
- Analysis (9 members)
- Analysis of the various types of mills (7 members)
- Anatomy (7 members)
- Andhra Pradesh (1 member)
- Android App Browser Testing (1 member)
- Animal husbandry (12 members)
- Animal power (8 members)
- Animals (34 members)
- Apiculture (2 members)
- Applied Thermodynamics (1 member)
- Appropedia (47 members)
- Appropedia's Public Domain Search (16 members)
- Appropedia, Appropedia Foundation (1 member)
- Appropedia Action Groups (0 members)
- Appropedia Foundation (11 members)
- Appropedia Help (1 member)
- Appropedia WordPress site (1 member)
- Appropedia administration (18 members)
- Appropedia archive (205 members)
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- Appropedia collaborations (18 members)
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- Appropedia guidelines (10 members)
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