This book is intended to primarily deal with detailed study of self-replicating code, "popularly" known as computer viruses.
There is an obvious lack of academic material available on this topic. It is indeed interesting how ingenious algorithms and techniques are being neglected by the academia in the name of legality.
A quine is also a kind of self-replicating automaton, except for the fact that rather than reproducing itself in the executable format, it produces as output the source code for the program.
For more details see quine program.
There has long been speculation about a self-replicating machine.
The RepRap Project is currently attempting to build the first generation of just such a device.
In 1986, Drexler suggested the possibility of grey goo.