Can I create a question that allows for a free answer (Essay)?

Yes, iSpring QuizMaker 6 provides you with such an opportunity. The essay question type can be used
in both graded quiz and survey modes. In survey mode you can simply click the "Essay" icon on the ribbon.

If you want to have an essay question inside your graded quiz, press the "Survey question" button on the ribbon
and choose "Essay" from the drop-down list.