• No ads
• No need to create a Google account
• Tools for managing subscriptions
• Adds ability to listen only to audio
• No need for YouTube app in order to listen to videos on mobile (or use Newpipe on Android)
• No need to "ding" bell, just being subscribed is enough to receive all notifications
• No age-gate
• Dark mode (although YouTube has this now too)
• Free software (AGPL v3 license)

A good Firefox add-on is Privacy Redirect. Apart from handling Youtube can also redirect other services, and it also automatically rotates each redirect from a list of Invidious instances so as to avoid overloading any single one.

See Invidious Instances for a list of publicly available instances.

• "Small acts of resistance are all we need. Together, we make change", Yarmo Mackenbach
• https://reddit.com/r/SideProject/comments/8wvazc/invidous_alternative_frontend_to_youtube/
• https://github.com/omarroth/invidious

Other Youtube front-end alternatives

• yt-dlp
• NewPipe (Android)
• PipePipe (Android), includes SponsorBlock
• yt-local , via reddit thread

Replacing Youtube altogether

Another approach is to replace Youtube with an open-source, federated video host service.
That would be PeerTube (see this blog post by LazyBear).

• https://fedi.video - a good place to get started with PeerTube, by FediThing

No coding knowledge required, very portable with Markdown text, and supports custom domains

Via Waxy.org

Images

• Creative Commons search engine that indexes over 300M CC-licensed images.
• Flickr Commons. An attempt to catalog the world's public photo archives.
• https://public.work - search engine of public domain images, via kottke.org and @holly_cummins@hachyderm.io.
• Openverse - search engine for openly licensed images, audio and more
• Unsplash. Fair warning, has started watermarking some photos.
• Pexels. Free-to-use (without attribution) stock photos, images and videos.
• Lexica - Stable Diffusion search engine. Search for images generated by the Stable Diffusion AI text-to-image model.

In related news

• https://www.flickr.org
• https://pechaflickr.net
• Google broke its image search. And hey CogDog, thanks for posting!
• https://cogdogblog.com/2022/12/flickr-fdn-thanks/

Text

• https://crowdview.ai - search engine that exclusively searches discussion forums

Scientific

• https://www.scienceopen.com/search (blog post)
• https://search.crossref.org
• https://scholia.toolforge.org (very cool - relies on WikiData, hosted on WikiMedia Toolforge)