ARSnova is a modern approach to Audience Response Systems (ARS). It is released under the GPLv3 license, and is offered as a Software as a Service free of charge. Head over to arsnova.eu to see it in action.
For the use of this interface you need an "ARSnova" account (authentication via the internal database) that is marked as an adminaccount in the properties
security.admin-accounts=<your account>
ARSnova is powered by Technische Hochschule Mittelhessen - University of Applied Sciences.