Geoboard Coordinate Plane

I found and used a program called Geoboard last week when teaching the students how to find
slope.  The Geoboard program let me drop and mark two points anywhere on a coordinate plane.
We used this when learning how to find the "rise" and the "run".  I could control what was going
up on the screen and could change directions when students asked, "How would you find slope if it looked like this?"  When they asked, I had them come up and drop two points on the coordinate plane.  We then as a class would talk about it and then find the slope.  I liked the program because it allowed the students to be involved and it allowed me to be flexible when choosing examples.