If you are a follower of my blogs then you know I swear by Remind101 and have a ton of people in my county now using it. But one of my teacher-students told me the other day about Celly which she loves to use to remind students. It has an added feature where she can poll students and get instant results even when they are not in class. Here are some examples for class use. Another cool idea they have is that they can keep a message stream going amongst the students so they could effectively form a study group after school (not that they aren't already using their phones!). Here are their how to guides.