After seeing no direct responses to this question, I'll instead be more direct myself. Ungrading is a buzzword being tossed about for assessing students' progress without focusing on quantitative feedback or letter grades, but instead emphasizing students' reflect on their own learning progress. Much of the discussion around ungrading is from instructors in the humanities. But math is different. At the very least, it's much tougher for students to assess their own correct understanding and learning progress in math.
How must the usual ideas of ungrading be adapted to work in a math class? How would the structure of a math class where the students receive no quantitative feedback have to differ from such a class in the humanities? Answers to this question certainly depend on the maturity of the students, so let's focus on undergraduate college students. For more information on ungrading, check out Jesse Stommel's How to Ungrade or Alfie Kohn's The Case Against Grades.