When consumers have been promised powerful, life-changing new software, delays and postponed launches can be excruciating.

Mac OS X was first demonstrated under the code-name Rhapsody in 1997, yet version 1 release didn't arrive until a full four years later. Windows Vista was originally planned to ship in 2003, as a minor release between Windows XP and the true follow-up, but that release date slipped by three years.

However, both of those pale in comparison to "Project Xanadu", which was released without fanfare at an event at California's Chapman University in late April. Development on Xanadu began 54 years ago, in 1960, making it the most delayed software in history.

Xanadu's developer Ted Nelson is the man who coined the term "hypertext" to describe the clickable links that were created for his project: the word lives on most prominently as the "ht" in the internet abbreviation "http".

At its simplest, Xanadu lets users build documents that seamlessly embed the sources which they are linking back to, creating, in Nelson's words, "an entire form of literature where links do not break as versions change; where documents may be closely compared side by side and closely annotated; where it is possible to see the origins of every quotation; and in which there is a valid copyright system - a literary, legal and business arrangement - for frictionless, non-negotiated quotation at any time and in any amount."

The version released on the internet, named OpenXanadu, is a simple document created using quoted sections from eight other works, including the King James Bible and the Wikipedia page on Steady State Theory. Users navigate with the spacebar and arrow keys – the directions warn users "don't touch the mouse!" - and can skip between the original works and the finished document.

Superficially, it resembles the web itself, and that's no coincidence. At one point, Xanadu had potential to beat Tim Berners Lee to the invention of the world wide web. But the project carried on slipping, and the web got there first.

"The web trivialized this original Xanadu model," Nelson argued in 2004, "vastly but incorrectly simplifying these problems to a world of fragile ever-breaking one-way links, with no recognition of change or copyright, and no support for multiple versions or principled re-use."

Having missed the chance to be the web, Nelson now sees Xanadu as a potential replacement for formats that spend too much time trying to be like paper, and not enough time trying to be something new for the digital age.

"We screwed up in the 1980s, and missed our chance to be world wide hypertext (the web got that niche). However, we can still compete with PDF, which simulates paper, by showing text connections."

In 1995 - with the project already 35 years in development - Wired's Gary Wolf profiled Nelson, painting a portrait of a man whose execution never caught up with his ideas. But those ideas themselves went on to become hugely influential.

"Out of Nelson's discombobulation was born one of the most powerful designs of the 20th century," Wolf wrote. "And Xanadu's goals - a universal library, a global information index, and a computerised royalty system - were shared by many of the smartest programmers of the first hacker generation".

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