Three square beams close into a loop that has no end. Seen along the (1,1,1) direction, the far end of the third beam lands exactly on the start of the first, so a solid that never closes reads as a closed triangle.
The panel names at the top right open the triangle, motion, and color panels. Triangle sets the length of a side, the thickness of the beams, how far the figure is turned, and how much of the screen it fills. Motion sets the travelling blocks, the speed, and whether it runs. Color sets the top face, the right face, the left face, the outline, the blocks, and the ground.
Drag the stage to move the figure and use the wheel to zoom; the field at the bottom right takes a zoom value too. Double-click a panel title to switch how the panels are laid out. In the movable layout you drag panels wherever you like and keep several open at once; in the fixed layout a single panel sits in the top right.