TodaysMeet is a great resource to get immediate feedback from the students if there is a quick question to ask or a KWL (What do you Know, What do you Want to know, What do you want to Learn). It allows students to be engaged and use their cell phones.
Poll Everywhere is easier to create and it also allows students to engage in quick questions using their cell phones. I really like this tool. Students will be so hooked on using this tool because they can use their cell phones.