A beautiful graphing calculator which can make complex maths look clear and simple, and don't miss the ready made lessons at "teacher.desmos.com"
This is a beautiful site which provides beneficial learning experiences in a range of maths (particularly aimed at lower secondary maths students).
I have found the internet connection needs to be strong and reliable for "polygraph" game, and some students "rush" through, unless guided. As the teacher you have a view of each student's progress, which I suggest you maintain to avoid students missing steps or making large errors.
How I Use It
Desmos is a great looking graphing calculator, that can make quite complex maths look simple.
One area that a lot of teachers miss (which is potentially the best part of the site) is teacher.desmos.com. This provides lessons which step by step learning experiences for student, through a "guess who" style interaction with other students or exploring the graphs of carnival activities. Students enjoyed and summary discussions demonstrated what they discovered.