We built a cross platform mobile clicker (student response system) based on Google App Engine. As one clicker is 50 dollars, and we don't have to use it all the time. So we built a mobile clicker which we could use the application web application or mobile applications. Professor no longer need to install software on their computer to host the vote for the questions. And students don't have to buy or take a clicker to participate in class discussion. All they need is to use their PC or mobile phones. Professor could set up a channel for students, and he could publish a vote for the class. And students who join the same channel could participate the voting. Different channel won't interact with each other. And there're direct feedback for the students.