Best for: Beginner extensive reading
Free graded readers from the Tadoku project: short illustrated books written for learners at different levels. Read them online, download them as PDFs, or watch them read aloud on YouTube.
NHK news rewritten in simpler Japanese with furigana and audio, aimed at learners and children.
Graded Japanese stories and articles with native audio, adjustable furigana and explanations of the grammar used. Some content is free; full access is paid.
Aozora Bunko: a free online library of Japanese books in the public domain, mostly older literature.
