An excellent tool for formative assessment is Google Forms. Good formative assessment allows you to be quickly responsive to student needs. Google Forms gives you the data from students instantly after they press submit. Since all student answers are together in one spreadsheet it is easy to quickly get a snapshot of how the students are understanding.
http://www.alicekeeler.com/teachertech/2015/06/04/google-forms-create-a-formative-assessment-quiz/