Search inside digitised books, browse the Internet Archive catalogue and read Wayback captures.
Free
Scanned where there is a package or repository to read, and every release diffed against the tool surface we already hold.
Search inside digitised books, browse the Internet Archive catalogue and read Wayback captures.
Search inside scanned US newspapers and browse the Library of Congress catalogue. No API key.
Search the BnF open catalogue: authors, works, editions and links to what is digitised.
Read IMSLP, the Petrucci Music Library: works, scores, editions, copyright. No API key.
Search the Internet Archive, the Library of Congress and data.bnf.fr at once, in one answer.