Comment by retorquere

I think citationsy addresses a different public -- it looks to be more like ZoteroBib (zbib.org) or the web-client of Zotero than Zotero Desktop. Citationsy is going to be convenient for one-offs, but it's very common to shop around a paper until it is accepted somewhere, or submit a follow-up paper that builds on an earlier one, and each outlet may have different citation style requirements. Tools like Zotero (and Mendeley) make that fairly easy because you can just switch the style and re-render the document, and you're (ususally) done. With citationsy, as far as I can tell, you'd need to revisit every reference in the paper to adjust it to the new style. And while it seems to have fallen out of favor, I don't think citationsy can do ibid-style referencing.