Source: https://xanadu.com.au/general/faq.html#2

Project Xanadu envisioned a universal hypertext system where documents were never copied, only referenced. Every quotation would remain linked to its source, every author would be credited, and every connection would be permanent. It sought to encode ethical authorship directly into the medium.

Although it never shipped as intended, Xanadu profoundly influenced how we think about links, attribution, and versioning. Its failure was less technical than systemic, but its ideas continue to resurface wherever people question the fragility and impermanence of the web.

Sharing what others dreamt before us as inspiration:

Every Xanadu server is uniquely and securely identified.

Every Xanadu server can be operated independently or in a network.

Every user is uniquely and securely identified.

Every user can search, retrieve, create, and store documents.

Every document can consist of any number of parts each of which may be of any data type.

Every document can contain links of any type including virtual copies ("transclusions") to any other document in the system accessible to its owner.

Links are visible and can be followed from all endpoints.

Permission to link to a document is explicitly granted by the act of publication.

Every document can contain a royalty mechanism at any desired degree of granularity to ensure payment on any portion accessed, including virtual copies ("transclusions") of all or part of the document.

Every document is uniquely and securely identified.

Every document can have secure access controls.

Every document can be rapidly searched, stored and retrieved without user knowledge of where it is physically stored.

Every document is automatically moved to physical storage appropriate to its frequency of access from any given location.

Every document is automatically stored redundantly to maintain availability even in case of a disaster.

Every Xanadu service provider can charge their users at any rate they choose for the storage, retrieval, and publishing of documents.

Every transaction is secure and auditable only by the parties to that transaction.

The Xanadu client–server communication protocol is an openly published standard. Third-party software development and integration is encouraged.[13]

Tumbler

In the design of the Xanadu computer system, a tumbler is an address of any range of content or link or a set of ranges or links. According to Gary Wolf in Wired, the idea of tumblers was that "the address would not only point the reader to the correct machine, it would also indicate the author of the document, the version of the document, the correct span of bytes, and the links associated with these bytes." Tumblers were created by Roger Gregory and Mark Miller.[3][14]

The idea behind tumblers comes from transfinite numbers.[3]