Category:Add-on

Per the Wikipedia usage, this category means to organize "snap-ins, plug-ins, extensions and themes" — generally all software elements which are designed to add to, enhance, extend or modify the functionality of a software application. In general, an add-on does not function as a stand-alone application, but only as an application component. See Wikipedia:Add-on, Wiktionary:add-on, Wiktionary:plug-in, Wiktionary:theme.