The venerable youtube-dl. (supported sites)

Always try this first, then look around for alternatives.

Make sure you're up to date though! (youtube-dl -U) YouTube likes to play a cat & mouse game, meaning youtube-dl breaks periodically… If a download errors out, there's a 95% chance you're just using an outdated version and it has been already fixed upstream (they make a new release every week or so).

Analoguous to youtube-dl, there's gallery-dl (supported sites)

For all zoomable images (Google Arts & Culture, hi-res scans, etc.), try https://dezoomify.ophir.dev/dezoomify/dezoomify.html (also has a standalone version)

• https://addons.mozilla.org/en-US/firefox/addon/hls-stream-detector/
• https://www.downloadhelper.net/
• https://www.downthemall.org/