Quine

A quine is a program which takes no input and produces a copy of its own source code as its only output.

In APL, a quine is listed in the FinnAPL idiom library as "an expression giving itself":

In 2019, Nick Nikolov proposed to shorten it using the commute operator:

Explanation:
 * the characters
 * reshape to shape 9, resulting in
 * concatenate with itself, resulting in
 * rotate one character to the left, getting the characters:

Further Entries
In 2022, APL Farm user OsKaR31415 shared the following: Explanation:

In this code, the main function is  with the right argument   being single quote literal (spelled with four quotes, , because single quotes delimit APL character literals, and quotes inside such must be doubled), and the left argument   being the character vector representation of the function.

The idea behind this quine is that the only thing you need to have a string containing the original code is to reproduce this structure: [quote] [function] [quote] [function] [quote] [quote] [quote] [quote]. This is precisely what the function does. Given the representation of a function  (itself in this case), and character   (here, the quote), it produces the structure. A more explicit version would be  which simply concatenates together the required parts. The original quine is very similar, only using the shorter  to produce the 4 occurrences of , and golfs away the spaces, instead opting for Enlist  to flatten the intermediary nested array.