Poll Everywhere captures live audience participation in the same way as clickers, but using the audience members’ own devices, whether feature phone, smartphone, tablet, or computer. It lets you engage your audience or class
anywhere in real time. Here’s a quick video introduction:

Alternatives to Poll Everywhere

All listed polling sites have a free option for basic use (unless otherwise indicated) and each also offers the option to pay for extended services

Poll Everywhere’s own comparison to its alternatives