Formative is one of my favorite free tools for conducting interactive formative assessments. I've used it to create image-based quizzes and diagram-based quizzes. You can also use it to create interactive assessments based on documents that you upload to the site.
Last week Formative announced via email that Formative 2.0 is coming soon. The new version will offer some outstanding new features. Before the new version is rolled-out on June 24th you should download any student responses that you think you'll want to be able to access in the new version. You can download all existing student responses in a CSV file. To do so, just go to the results page of any assessment and select "export." Selecting the export option will generate a CSV file that you can download and later import into the next version of Formative.