Bip39 Private Key Recovery Tool. From this level ahead the seed may be prepared on paper or spoken above phone and this opened up new, Actual physical means of backing up the seed (several paper copies in different destinations, sturdy copies on steel plates with excess protection from fire/flood etc.). https://griffinalvfp.hazeronwiki.com/7437207/the_anatomy_of_a_bip39_phrase_entropy_terms_and_safety