Epilogue

The background details of Poul Anderson's "Epilogue" (Explorations, New York, 1981) include three ingredients that seem very familiar to regular Anderson readers:

a global conflict, this time with "Panasia" instead of with "Unasia";
fifty scientifically trained couples leaving Earth to colonize Tau Ceti II;
a malfunction in their faster than light (FTL) spaceship, the Traveler.

Because of the malfunction, the Traveler returns to Earth three billion years later but with an unaged crew, a time dilation effect although in what was meant to have been an FTL ship. (Correction, 6/8/13: This was meant to have been a NAFAL, nearly as fast as light, ship.)

Then the story starts. It is told in seven sections -

I, viewpoint character: a being called "Zero";
II and III, viewpoint character: Hugh Darkington of the Traveler;
IV, Zero;
V, Darkington;
VI, Zero;
VII, Darkington.

Zero's real name is"...a set of radio pulses..." that would be "...an ugly squawk..." as sound so the omniscient narrator decrees that he be called "Zero" because, like every conscious being, he is "...the center of his own coordinate system..." (p. 177). Thereafter, others of his kind are given, purely for the reader's benefit, numbers from One to Hundred.

Although the Traveler crew needs most of the story to deduce what has happened, it soon becomes clear to the reader that Zero and the like are conscious robots surrounded by inorganic, metallic equivalents of trees, flowers, insects, birds etc - a "mechology"?

Metal shafts rising from sand and supporting girders bearing solar energy accumulators have replaced tree trunks rising from soil, supporting green leaves;
crystalline growths containing wires, coils or transistors have replaced smaller plants;
fliers have replaced birds;
"aquamotiles" have replaced fish.

In Anderson's Technic Civilization History, Dominic Flandry once met predatory robotic animals but those had been designed as a pass-time by a consciousness-level computer whereas these have evolved by natural selection from originals constructed by now extinct Terrestrial humanity. Zero and co transmit sense impressions and share rituals, science, poetry etc, so they do more than merely survive. Since Earth is now theirs, the returned human beings must go elsewhere.