Below is a list of useful scripts in Geometer's SketchPad

Centroid	Orthocenter	Circumcenter / Circumcircle
Incenter/Incircle	Medial triangle	Orthocenter, Mid-segment triangle
Orthic triangle	Triangle centers with Euler Line	Center of Nine point circle
Trisecting a line segment	Equilateral triangle, given a side	Square, given a side
	Triangle centers (H, G, C, and I)