Ignoring the intentionally esoteric languages, of languages in actual use:
J, K. Any descendant of APL, basically, and APL itself, though arguably APL is less obtuse than many of its descendants.
E.g, quicksort in J (EDIT: Note Lemmy seems to still garble it despite the code block; see the Wikipedia page on J for the original and other horrifying examples)
Ignoring the intentionally esoteric languages, of languages in actual use: J, K. Any descendant of APL, basically, and APL itself, though arguably APL is less obtuse than many of its descendants.
E.g, quicksort in J (EDIT: Note Lemmy seems to still garble it despite the code block; see the Wikipedia page on J for the original and other horrifying examples)
quicksort=: (($:@(<#[), (=#[), $:@(>#[)) ({~ ?@#)) ^: (1<#)(No, I can not explain it to you)
https://www.rosettacode.org/wiki/Category:APL and https://www.rosettacode.org/wiki/Category:J for fun links.
Traditional APL required its own typewriter ball for printing out programs.