Open-source implementation of the K programming language
Kona is the open-source implementation of the k3 programming language. k is a synthesis of APL and LISP. Although many of the capabilities come from APL, the fundamental data construct is quite different. In APL the construct is a multi-dimensional matrix-like array, where the dimension of the array can range from 0 to some maximum (often 9). In k, like LISP, the fundamental data construct is a list. Also, like LISP, the k language is ASCII-based, so you don't need a special keyboard.