Unlicense

Arto Bendiken published it at unlicense.org on 1 January 2010, as a protest against licence debates eating more time than the code. The first paragraph dedicates the software to the public domain, the next lets anyone do anything with it, and the usual all-caps warranty disclaimer closes things out. It fits on less than a screen, and it was written by a programmer rather than a lawyer.

That is also the core of the criticism. Lawyers have pointed out that it mixes a waiver and a licence without saying what applies when one of them fails, something CC0 spells out carefully. The OSI approved it anyway in 2020. If you want certainty, pick 0BSD or CC0; if you just want people to stop asking, pick the Unlicense and accept that some corporate counsel will ask regardless.