Sint '98: original version of Sint Nicolaas for DOS (written in 1998)

Wiering Software: creator of several fun, non-violent, low-end PC games

Clean: functional programming language used to create Sint Nicolaas and Zwarte Piet

Clean Game Library: complete library for creating all kinds of 2D games in Clean

Tile Studio: free tile/sprite/map editor for tile-based games with programmable output

POVRay: this free ray-tracing program was used to render the graphics of Zwarte Piet