Kona is the open-source implementation of the K 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. For many people, K was the preferred APL dialect. When it was available, it tended to be popular with investment bankers, the performance obsessed, and analysts dealing with lots of data. It is a demanding language.