From The Free On-line Dictionary of Computing: (http://www.foldoc.org/, Editor Denis Howe)
A derivative and redesign of APL with added features and control structures. J is purely functional with lexical scope and more conventional control structures, plus several new concepts such as function rank and function arrays. J was designed and developed by Kennneth E. Iverson and Roger Hui hui@yrloc.ipsa.reuter.com. J uses only the ASCII character set but has a spelling scheme that retains the advantages of APL's special alphabet. J is a conventional procedural programming language but can be used as a purely functional language.
Version 4.1 for MS-DOS, Sun, Mac, Archimedes. Source available in C from Iverson Software, +1 (416) 925 6096.