I donate to Internet Archive every year because it's such an amazing resource. Not only do they have the Wayback Machine for viewing historic snapshots of web sites, but they have a lot of other content too.
For many of the wildlife conservationists I support, they have to make do with older hardware for a lot longer than for-profit orgs. This can be a problem when needing to reinstall an older operating system.
But the Internet Archive hosts copies of these old installers! Here's High Sierra and El Capitan. And best of all, they support download via Torrent, which makes it so much more resilient when downloading large files over unreliable internet connections.