I am fairly certain that you have heard of Kahoot! It is a really easy quiz site that is amazingly friendly with just about any device. My students love it because they can use their phones, tablets, Ipads, Chromebooks, or just about anything else to participate. I don't know why, but the idea of using their own device as opposed to one of our classroom devices makes it infinitely more appealing to them.
Did you know that Kahoot! provides your with data afterwards? After you have given a quiz you can instantly download the results of each student's response in an Excel file. This makes it amazingly easy to see where students are thriving, and where they need a little more assistance. If you are not using this function of Kahoot! yet you are missing out!
Plickers is a fantastic app to use if you are limited on devices because it only takes one! Each student has a QR code that they hold in a certain direction to answer the question. You can read more about it here.
Like Kahoot! Plickers also has an aspect that allows you to look at the data afterwards, but unlike Kahoot! you also get real time data as students answer the questions!
Baiboard is a great app for working collaboratively to check for understanding. I love that this app allows students to work together and check up on each other's thinking.