gallery-dl is a command-line program that allows you to download image-galleries and collections from 100+ image hosting websites, including 500px, Behance, DeviantArt, Flickr, Gfycat, imgur, Instagram, Reddit, Tumblr and Twitter. It is a cross-platform tool with many configuration options and powerful filenaming capabilities.
gallery-dl also supports user authentication via OAuth for deviantart, flickr, reddit, smugmug and tumblr. This is entirely optional, but grants gallery-dl the ability to issue requests on your account’s behalf and enables it to access resources which would otherwise be unavailable to a public user.
For a full list of supported websites and instructions on how to install gallery-dl on your machine check out the official project page on GitHub.