The Babel Nexus Index is a free, visual way to explore the great public-domain books — the classics whose copyright has expired, so anyone can read them. Instead of a search box and a flat list, it lays knowledge out as a map of connected rooms: each room is a subject, each book sits on a shelf inside it, and lines between rooms show how one field of thought led to another.
It holds no files of its own. It is a discovery index — every book links out to the original library that hosts it (Project Gutenberg, the Internet Archive, Wikisource). You can read any work in place, ask the built-in Oracle a question and get answers drawn only from these books, or stitch rooms into a shareable Reading Trail. No account, no cost — only anonymous, aggregate analytics.