Two rounds of phone interviews + completing the Challenge.
I came via employee referral and the Medallia team was professional throughout. The initial HR screen was slightly adversarial, but fair and covered what one would expect - in other words, a good first step. The interview (again phone) with the hiring manager was very positive, and again covered the right ground for my qualifications and some cultural fit.
The next step was to complete the Challenge (others have commented, I won't go into detail). I would have preferred to actually meeting face-to-face with the hiring manager before this step, as it does represent an investment of time and effort on my part (and of course on their part as well); that said, I was very interested in the company and you are given only 24 hours to complete it, so the time spent isn't too bad. (Other companies give you a week or even more for case studies; I don't know if that is in part to test your stamina, but it smacks a bit of hubris.) I received only limited feedback from HR on the Challenge and had to ask for it, but was told I did well.
The position was ultimately filled by an internal candidate. This was disappointing, but they were prompt in telling me which I appreciated. Warning to job seekers: I have had more than one internal candidate raise their hand, and it is good to ask some initial questions on this front.