However, it seems not to have been maintained for several years and some of the links may no longer work, although just about all of those that I clicked on were still good.
Another useful site is Gateway to the Classics, a database of online books, poetry and stories for young people. Ebook versions of the materials are for sale but they can be read on the site for free. The site is searchable by author, title, and type of material (books, poetry, stories, even nursery rhymes). Information for each item includes date of publication, grade level, and genre.
And millions of books, videos, archived websites, etc. are available on the Wayback Machine, which has been in existence since the late twentieth century.
Try the Khan Academy. It’s free and offers every course imaginable.