Esoteric programming languages

An esoteric programming language (sometimes shortened to esolang) is a programming language designed as a test of the boundaries of computer programming language design, as a proof of concept, or as a joke. There is usually no intention of the language being adopted for mainstream programming, although some esoteric features such as visuospatial syntax have inspired practical applications in the arts. Such languages are often popular among hackers and hobbyists. This use of esoteric is meant to distinguish these languages from more popular programming languages.
Usability is rarely a high priority for such languages; often quite the opposite. The usual aim is to remove or replace conventional language features while still maintaining a language that is Turing-complete, or even one for which the computational class is unknown.