A friendly PSA, given how useful these kind of programs are:
Command-line program that lets you mass-download art from a LOT of different sites by just typing "gallery-dl [URL]" into Command Prompt. So far I've successfully used it to download from FurAffinity, Inkbunny, e621, pixiv, e-hentai, Twitter, and DeviantArt. You can even pull posts from Kemono, although you need to specify cookies in a gallery-dl config file in order to get around the DDoS protection. You can also pull directly from a paysite like Patreon or SubscribeStar if you import your session key into the config file.
Rule34.xxx Downloader (https://github.com/r34dlnew/Rule34.xxx-Downloader
gallery-dl unfortunately doesn't work for rule34.xxx. This one does, though, with the added benefit of being able to choose whether or not to download images, gifs, and videos individually.
Twitter Media Downloader (https://addons.mozilla.org/en-US/firefox/addon/tw-media-downloader/
Firefox extension (I think it's on Chrome too) that lets you both download images from individual twitter posts and mass-download all of a user's Media, Likes, and/or Retweets.
Use this thread if you have any questions about these kinds of programs, or if you know of any others.