Excellent Form Plug-in

This is by far the best free-mium form plug-in. It is reliable, highly customizable, and has a bunch of features and integrations. The quizzes are great and I use them constantly. If you are looking for pop-ups or embeds, check out Hustle, also created by the same developers and also awesome. If you are just starting out, check out the pro license; it covers a ton of must have plug-ins you will need if you are trying to run create a small web based business. These guys/ gals really get it and make amazing stuff.