Quine

A quine, named after the philosopher W. V. O. Quine, is a program that prints its own source code. One of the typical challenges of any new esoteric programming language is to write a quine other than the null program in it.

Often a program that just performs access to its own source code (reading it either from memory or from a disk file) and prints it out is considered "cheating".

The language Muriel is based on the idea of quines.

External resources

 * The Quine Page has a nice collection of quines in different languages.
 * Quines (self-replicating programs) is excellent information about quines.
 * A truly esoterical quine