I have to list three: DataVision (http://datavision.sourceforge.net) because it's in use in fifty countries, a version of Objective-C I called Subjective-C (1996) because it taught me about parsing and runtime stack manipulation, and a Java applet-based image manipulation package that let you apply makeup (eye shades and lip shades, with added gloss) to your own photo on the Web back in 1999, because it was ahead of its time.