classEx: An online software for classroom experiments

classEx is a novel software that allows lecturers to carry out experiments in the classroom with an instantaneous graphical illustration of findings. Standard experiments with multiple treatments, monetary incentives, roles, groups, rounds and stages are available in a ready-made format. A back end allows more sophisticated users to implement their own experiments. We present examples, describe the architecture and show how the design can be tailored to become useful for research.