I read a tweet yesterday about Geddit being a new Formative Assessment tool. Being as how I have used 6 others, I figured that this would fit into the realm of just like the others with a nuance here or there. From the formative assessment tools I have used, this is my favorite, if you are willing to front-load a little work (inputting your students).
You can choose to have students enter a code upon signup . This is a feature that works great with other programs, but I can see how this would be an issue with this program. As a teacher you have a single code. When a student enters your code, they choose which of your classes to enroll. I would rather sidestep this and get a list of full names and usernames for students and input them myself, probably using a google form and a bunch of copy and paste.
Questions and Lessons. Through this app there is the option of making questions that students can answer (multiple choice, text, long text, and poll) where you can formatively assess students throughout the lesson. This is also the only tool like this, that I have found, that has an equation editor. The lesson is a cool feature. Questions are organized into a lesson that you create and you can adjust the order of the questions in a lesson, ask all or some of the questions now (meaning that students will see the questions when they join the class) or ask questions later (meaning they only appear when you click ASK in the app.
Aside from that, there is the self evaluation aspect of Geddit. Students can check in at any time to let you know if they are lost or if they are getting it. They can also raise their hand at any point on their screen and you will see that they need attention. I thought this was a great feature as students can respond to what you are doing even if you are not asking them questions. Promoting proactive learners.
Lesson Data. When you finish the lesson and hit end, there is a great amount of data presented to you. You can see how all students have done in your class, you can see question data, response frequencies, check-in data, check-in data throughout the time in class to see if students moved toward understanding or not. You can share data with students, you can see who had trouble with the lesson versus who had ease in learning material. You can export the data, but I did not find that very helpful, I liked the data visualizations online. Give it a try.