On Periodo Fertile me and my wife decided to publish some quizzes on pregnancy and fertility. Having no time to create a quiz plugin I searched between the free ones just to have a quick start.
I found WpProQuiz, and it is incredible. It lets to create as many quizzes as you want with an infinite number of options which at start can be overwhelming but they cover every need.
The you will move into the questions and the answers. Every question can be configured to the little details: appearance, point calculation, single or multiple answers, visual editor to edit the question so you can enrich it with images and links. After the answer you can show a text with explanations about the question and the correct answer.
The style is a little bit old, but with few CSS rules the design can be easily improved (or you can ask the authors who are available for customization).
Quizzes can be embedded inside any post or page with a simple short code. Answers can be collected from registered users or even anonymous users. Statistics are collected and available on the admin side, but mean values can be shown to the users as well.
Definitively, if you’re looking for a quiz plugin for WordPress, try WpProQuiz.