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)
- Appropedia books (0 members)
- Appropedia bots (14 members)
- Appropedia collaborations (18 members)
- Appropedia communication (3 members)
- Appropedia communications (6 members)
- Appropedia community (3 members)
- Appropedia content (5 members)
- Appropedia guidelines (10 members)
- Appropedia help (62 members)
- Appropedia internships and volunteering (10 members)
- Appropedia logos (3 members)
- Appropedia maintenance (0 members)
- Appropedia policies (16 members)
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- 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)
- Appropedia site tools (10 members)
- Appropedia user interface (2 members)
- Appropedians (0 members)
- Appropedians in the United Kingdom (0 members)
- Appropriate Technology Sourcebook (342 members)
- Appropriate technology (586 members)
- Appropriate technology advocates (8 members)
- Appropriate technology demonstration events (2 members)
- Appropriate technology events (7 members)
- Appropriate technology files (36 members)
- Appropriate technology organizations (35 members)
- Appropriate technology videos (105 members)
- Appropriate technology villages (2 members)
- Appropriate textile production manual (0 members)
- Aquaculture (24 members)
- Arcata Educational Farm (25 members)
- Arcata Marsh (37 members)
- Arcata marsh files (127 members)
- Arcata marsh images (0 members)
- Archery (1 member)
- Architecture (20 members)
- Archived pages (0 members)
- Arctic (2 members)
- Arduino (3 members)
- Are You Ready? (40 members)
- Are You Ready? An In-depth Guide to Citizen Preparedness (30 members)
- Argentina (47 members)
- Armenia (2 members)
- Art (5 members)
- Articles (6 members)
- Articles in need of copyediting (0 members)
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- Artikel auf deutsch (2 members)
- Arts, sport and culture (7 members)
- Arts, sport and culture by location (4 members)
- Arts, sport and culture files (4 members)
- Arts, sport and culture images (0 members)
- Asia (41 members)
- Asia files (32 members)
- Asia images (0 members)
- Assistive Devices (3 members)
- Asthma (6 members)
- Athena (48 members)
- AthenaII (17 members)
- Athena II (1 member)
- Athena mods (1 member)
- Attribution (1 member)
- Australia (78 members)
- Australia files (10 members)