Cite with Reference Tooltips
I don't think it was done as a gadget other than my version, though I could be mistaken. (I might also be misunderstanding what counts as a "gadget".)
The English Wikipedia community is currently discussing whether to enable the Reference Tooltips gadget by default at w:WP:VPR#Reference Tooltips. (It was covered in the Signpost a bit ago, and has been in the Centralized Discussion for a while.) While I personally am in favor of leaving the issue of whether/how to enable a ReferenceTooltips feature up to the community, I understand that the Wikimedia Foundation often makes major changes without getting consensus first. I hope that if the WMF does enable the feature that the community is at least informed ahead of time. If the WMF isn't going to go around the community, and the community supports the feature, it will probably be implemented as a gadget (and thus under the community's control), so it wouldn't be necessary to integrate in into Werdna's extension addition.
As I mentioned in response to your post on my Mediawiki talk page some weeks ago (I assume you didn't see the response), I much prefer communicating on-wiki instead of using email. I hope that is acceptable. My Mediawiki talk page isn't the "wrong" talk page, by the way; I frequently check my Wiktionary, Wikipedia, Meta, and Mediawiki talk pages and contacting me through any of them is perfectly fine.
(Since you probably won't be checking Wiktionary for a response soon, I'll go leave a talkback on your MW and Meta talk pages.)
Apologies into thinking yours was anything other than a gadget.
I would prefer extensions simply because gadgets aren't consistent across wikis and are prone to breakage when the underlying HTML changes. What I wanted was to incorporate the HTML/CSS in your gadget into the reference tooltips in the Cite extension since it is closer to the reference design.
As for the WMF changes without consensus. This was not the case here. The reference tooltips in question was made long before any consensus was reached. The issue was timing with the release process made it look this way because code made months before wasn't set to default on until much later. :-( It is a sad issue that "informing the community" is different between information of this on MediaWiki (where it's been for ages) and the en wiki community.
Oh well, if it's enabled as a site-wide gadget I'm not going to cry about it. However, if you could work with User:Werdna at getting the Cite extension UI up-to-date that'd be nice-for the other wikis.