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:

    quicksort=: (($:@(<#[), (=#[), $:@(>#[)) ({~ ?@#)) ^: (1<#)

(No, I can not explain it to you)