Seldon's plan is a future map of humanity, from the collapse of the first galactic empire to the establishment of the second, a thousand years in the future. It is developed according to psychohistory, and named after the father of this new science and of the plan itself: Hari Seldon. Psychohistory is a kind of statistical mechanics to predict the behaviour of large populations, and using the plan a secret organisation shapes the destiny of the galaxy towards this Second Empire. The seed of the future empire is a society named the Foundation, on a planet named Terminus, and the secret organisation - tasked to improve the plan and from its hidden vantage point manipulate humanity - is called the Second Foundation, unknown by the first and established by Seldon himself.
This story is told in the science fiction books of the Foundation series by Isaac Asimov, a space opera classic.
What fascinates me is the user interface by which the Plan is read and explored by "Speakers" -- the secret members/academics/bureaucrats of the Second Foundation. It is projected on the wall as a network of dense, interlocking equations by a device named the "Prime Radiant," and manipulated using a combination of gestural interface and thought control. Black equations were part of the original Seldon plan; red is used for those added by Speakers; blue is where unanticipated deviations from the plan have occurred.
I've taken two extracts which describe the Prime Radiant and the visualisation of the Plan from the books Second Foundation and Foundation's Edge. Read the extracts here.