bogusforth - - Obfuscated language, powerful, quite complete, unmaintained, based on forth, "false" (by W. van Oortmerssen), and "TRUE" (by Dewi). By Antonio Maschio.
Cat's Eye Technologies - - Specifications, implementations, sample source code collections for several strange languages, comments on obfuscated language taxonomy and on several far-out coding practices, mail list, links to many related sites.
Esoteric Non-existent Standards Institute - - "Institute" for the standardization of unstandardized standardizable things, mostly esoteric languages and extensions to them.
esoteric.sange.fi - - Collection of esoteric programming language implementations, examples, and related files.
False - - Programming language with two main goals: confusing everyone with an obfuscated syntax, and designing as powerful a language as possible with a tiny implementation: this compiler executable is only 1024 bytes, written in pure 68000 assembler.
l33t - - An esoteric language inspired by BF and Beatnik which allows l33t h4xX0r5 to write programs in their native dialect.
nouse - - A language in which the IP (instruction pointer) varies depending on the current stack size.
npiet - - An interpreter for the piet programming language. In this language the programs are pictures, build out of 18 colors and black and white - this is about the real "art of programming".
Orthogonal - - A programming language in which program flow can go sideways. Closely related to Befunge. Tutorial, reference, sample source code, Public Domain implementation available.
Owl - - Obfuscated Weird Language: character-based language interpreter written in C, in the style of False. By Antonio Maschio.
P-nand-Q - - Home of esoteric programming languages such as Java2K, Smith#, Sorted!, [], Esogotschi and the Great Python Language Zoo. Also heavy on the code obfuscation front.
Programming in Malbolge - - Introduction to Malbolge programming. Also propose modificatins of Malbolge for making programming in it more worse.
Q-BAL Programming Language - - A queue based programming language. It's not designed to be useful, just fun.
Shakespeare - - A language with beautiful source code that resembled Shakespeare plays.
Turing Tarpit - - Directory of sites dealing with obfuscated programming languages.
The Unlambda Programming Language - - Minimalistic functional language based on the Lambda calculus but lacking the Lambda operator. Tutorial, reference, GPLed interpreters available.
Waduzitdo - - Turing incomplete programming language written by a guy named Larry, who's friends always asked him about his new PC: "What does it do?" Works via 2 registers: accumulator and match flag which holds one value (T or F).
Whitespace - - Any non whitespace characters are ignored; only spaces, tabs and newlines are considered syntax.
XS: XML-based Obfuscated Programming Language - - Toy language. Harness the power of XML, by using it as a programming language. Compiler, sample code; interesting speculations on language design. By Mark Carter.
ZT - - The esoteric programming language. Documentation, interpreter, and example programs.