Wisdolia

Wisdolia is a browser extension that turns whatever you are reading or watching — an article, a PDF, a YouTube lecture — into question-and-answer flashcards without leaving the page.

Its value is in testing recall rather than re-reading, which is what actually moves material into memory. The cards it writes are only as good as the source, though: it will happily turn a vague sentence into a vague card, so review the deck before you study it.