Geoboard

Press a button and drag the mouse to create vertices and the sides of a square grid shape. To delete a node, check the "Delete nodes" and then click on undesirable nodes. Check back the "Draw nodes" box when finished.

This applet requires Sun's Java VM 2 which your browser may perceive as a popup. Which it is not. If you want to see the applet work, visit Sun's website at http://www.java.com/en/download/index.jsp, download and install Java VM and enjoy the applet.