Fill and pour - the 'jugs' problem: given two jugs of various capacities, how can you create a third amount?
How high? - pour liquid from one container to another, how high will it go? Can involve volumes of cuboids.
Could involve volumes of cuboids, cylinders and cones (illustrating that a cone is a third of a surrounding cylinder)
Grapher -set up a general quadratic ax^2 + bx + c and see the effect of changing each parameter (with a slider)
Line plotter -given a point and the gradient of the line, construct and check the line's position.
Platonic solids - what's the minimum numbers of colours needed to colour faces of the platonic solids so that adjacent faces are different colours?