K

K, by Arthur Whitney, is a propretary collection-oriented programming language (see also its companion Kdb, a DBMS written in K) descendant of APL and A+ with some influence from Lisp, especially suited to time-series analysis (financial application, insurance and other industries). A couple of interesting articles from Kuro5hin:

A Shallow Introduction to the K Programming Language (in a better format here at his web pages), by Jayson Nordwick.
The K tree, by Cal Jayson.

Jayson Nordwick Slashdot post:

What about K?.

A system based on K:

K.CoSy, by Bob Armstrong.

The K company:

Kx Systems, Inc..

cK is Concatenative K, a Joy-style concatenative syntactic overlay for the K programming language.
tcK is tiny concatenative K.
K for Joy Programmers.
Unlambda in K.
Befunge-93 in K.
False! in K.
BrainFuck in K.
Befreak in K.

This page is linked from: CoSy Glee Syntax in K TUI