Wikipedia:Gadget

A Wikipedia gadget is a JavaScript program and/or a CSS snippet that can be enabled simply by checking an option in your preferences. The gadget's function is provided by the MediaWiki extension Extension:Gadgets.

Wikipedia data structure
Subject namespaces Talk namespaces
0 (Main/Article) Talk 1
2 User User talk 3
4 Wikipedia Wikipedia talk 5
6 File File talk 7
8 MediaWiki MediaWiki talk 9
10 Template Template talk 11
12 Help Help talk 13
14 Category Category talk 15
100 Portal Portal talk 101
118 Draft Draft talk 119
710 TimedText TimedText talk 711
828 Module Module talk 829
Deprecated
2300 Gadget Gadget talk 2301
2302 Gadget definition Gadget definition talk 2303
-1 Special
-2 Media

Many gadgets started out as user scripts. Once a user script is approved as a gadget, it is removed from Wikipedia:User scripts/List.