My daughter-in-law introduced me to this site. It is free and my students enjoyed using it. You can put a power point on the site and insert polls or quizzes for the students to take as they move through the powerpoint. You can decide if you want to do the lesson as a class or have the students do it at their pace. You get reports that give you the quiz grades and a participation grade. I teach a repeater class and they were engaged the whole lesson. (Well most of them)