PS/Tk stands for a portable Scheme interface to the Tk GUI toolkit. It has a rich history going all the way back to Scheme_wish by Sven Hartrumpf in 1997. Wolf-Dieter Busch created a Chicken port called Chicken/Tk in 2004. It took on its current name when Nils M Holm stripped it of Chicken-isms to make it portable amongst Scheme implementations in 2006.