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.

http://www.theguardian.com/technology/2014/jun/06/vapourware-software-54-years-xanadu-ted-nelson-chapman