I've been using Calibre to download books and fics lately and even though I only use it in a very simple manner (it is capable of far more than I have a clue about doing) I am loving it.
Of course, for fic, it pretty much requires the FanFicFare plugin. Or, I guess require is a bit strong. But it makes downloading from AO3 soooo fucking easy. Well. With a couple work arounds because of Cloudflare, but the github page has the main ones listed. And there's also the forum that FFF creator uses to post updates and stuff that also has answers for resolving any issues.
Like it especially for fic, because it will bring all the meta data, including tags and archive warnings, with the fic. Which is the big reason I like it better than just using the native download options for AO3.
FFF makes updating WIPs really easy, too.
But, what really prompted this is fairly recently they added the ability to have snippets that can be added to the personal.ini just for a specific download instance that can override other sections without have to be a permanent change to the ini.
So now I can download fics that have a workskin and make the download keep them. Yeeessss! It was pretty exciting to go test that out and then launch the downloaded fic and see the same stuff I see on AO3. :D