Poll Everywhere lets you engage your audience or class in real time. Ask your audience a question with the Poll Everywhere app. Audience answers in real time using mobile phones, Twitter, or web browsers. See your response live on the web or in a PowerPoint presentation. Poll Everywhere replaces expensive proprietary audience response hardware with standard web technology.
As of now, DirectPoll is free and is likely to remain free in near future. Additional paid features may be added later-on but the basic service is likely to stay free. Currently, there's a limit of 500 concurrent voters on polls.Polling Tools DirectPoll