They send user information to a third party site (addthis.com).
Some have been removed, e.g.
https://kk.wikipedia.org/w/index.php?title=%D0%9C%D0%B5%D0%B4%D0%B8%D0%B0%D0%A3%D0%B8%D0%BA%D0%B8:Gadgets-definition&diff=2553369&oldid=2553242
Others remain:
```
$ mwgrep addthis.com
arwiki MediaWiki:Gadget-Sharebox.js
avwiki MediaWiki:Gadget-addThisMain.js
cewiki MediaWiki:Gadget-addThisArticles.js
cewiki MediaWiki:Gadget-addThisMain.js
hewikivoyage MediaWiki:Gadget-Sharebox.js
pswiki MediaWiki:Gadget-sharebox.js
ruwiki MediaWiki:Gadget-addThisArticles.js
ruwiki MediaWiki:Gadget-addThisMain.js
ruwikisource MediaWiki:Gadget-addThisArticles.js
tgwiki MediaWiki:Gadget-addThisArticles.js
tgwiki MediaWiki:Gadget-addThisMain.js
udmwiki MediaWiki:Gadget-addThisArticles.js
urwiki MediaWiki:Gadget-sharebox.js
```