A list of available instances can be found here.
Invidious has no advertisements. If you share an invidious link you can rest comfortably knowing the recipient(s) are not financially benefiting Google.
Invidious provides Atom feeds and an internal subscription system.
There are several extensions such as Invidition and Privacy Redirect which automatically redirect YouTube links to Invidious instances.
The Peertubeify extension can redirect Invidious links to the same video hosted on Peertube if available.
Nitter is another project that does the equivalent for Twitter.