Some people found the earlier iteration of this post useful. I've now updated the sites from around 50 to 86.
What the list is:
Designed to support pupils and students on a learning journey: it's about discovery, thinking and learning for its own sake
Websites, not apps, though there are a few YouTube links
Probably most useful to secondary schools and colleges
Trying to list some sites, or parts of sites, which have now become free. Subscriptions have been suspended on a number of sites
Designed to encourage Active Listeners and Active Responders via Google Classroom, or any format you consider appropriate - or indeed, none.
What the list is not:
Comprehensive: it's just a sample
Designed to cover every subject or curriculum area
About revision sites, recall or retrieval practice
You are welcome to share it, borrow it, steal it and improve it. The list is here.