This website makes it easy to create polls to ask formative assessment questions.
The polls are easy to set up but students do need a device to use the polling system. They either need a phone with texting, twitter access or a device with a web browser. Students have sometimes had a hard time understanding the directions with texting because they have to text a code to a particular number in order for it to work. Once they get it though, it's a fun way to get a sense of what they are thinking.
How I Use It
I've used it for an activator and for formative assessment. It is easier to set up than other polling software and doesn't require clickers.