The following categories exist on the wiki, and may or may not be unused. Also see wanted categories.
- Surveillance (2 members)
- Survival (24 members)
- Sustainable (13 members)
- Symbols (2 members)
- Syndication (1 member)
- TCL (10 members)
- TV (2 members)
- Tablatures (1 member)
- Template:Lizenz für Bilder (0 members)
- Templates (6 members)
- Timothy Leary (13 members)
- Ting (106 members)
- Tips (1 member)
- ToDo (1 member)
- Trading (1 member)
- Travel (1 member)
- Twitter (1 member)
- UFO (3 members)
- UNIX (27 members)
- USA (5 members)
- Under Construction (103 members)
- Units (1 member)
- Unix (52 members)
- Urban Legends (6 members)
- UseMod (3 members)
- VRML (3 members)
- Veritas (1 member)
- Voice (11 members)
- Vollmondtage (13 members)
- VxVM (1 member)
- Wallpapers (1 member)
- Web (3 members)
- Webdesign ? (1 member)
- Websites (132 members)
- Wiki (237 members)
- WikiCulture (1 member)
- Wiki Calendar (2 members)
- Wiki hives (9 members)
- Wikilandia (6 members)
- Wikimania (2 members)
- Wikimedia Commons (14 members)
- Wikimedia Projects (16 members)
- Wikipedia Asyl (1 member)
- Wikistats (41 members)
- Window Managers (6 members)
- Windows (76 members)
- Windows processes (2 members)
- Women (5 members)
- X3D (2 members)
- Yoga (81 members)