Here are some examples of simple applets. Have a try and suggest some questions that can be asked about each one.

Perpendicular SidesHere is a simple quadrilateral ABCD. Can you make
How would you extend this problem to a hexagon? This is a task adapted from Watson & Mason (2005) p.161. 
Square and Reflection
Point E is reflected on four sides of a square ABCD. What do you know about the quadrilateral formed by the images of E (red points)? Drag E to test how the quadrilateral may change. In what ways some properties are independent of position of E? (Do you drag E outside the square?)
Click the 'show' button to reveal the quadrilateral.
Click the 'show' button to reveal the quadrilateral.
What special quadrilaterals can the four red points form (such as parallelogram, trapezium, kite)? Where should you place point E to make those special quadrilaterals?
Try a similar investigation by beginning with another quadrilateral, instead of a square. Do you expect any difference in the behaviour of the resulting quadrilateral? In what other ways can you extend this investigation?
Try a similar investigation by beginning with another quadrilateral, instead of a square. Do you expect any difference in the behaviour of the resulting quadrilateral? In what other ways can you extend this investigation?
Make a Symmetric Pentagon
Drag any vertices of this pentagon to make it symmetric.
Suppose the vertices are only placed on the grid points. In what ways this pentagon can be symmetric? How many axes of symmetry will it have?
Can you make a symmetric pentagon without any side parallel to the grid lines? How can you test whether the pentagon is symmetric?
Suppose the vertices are only placed on the grid points. In what ways this pentagon can be symmetric? How many axes of symmetry will it have?
Can you make a symmetric pentagon without any side parallel to the grid lines? How can you test whether the pentagon is symmetric?