* Working for free because it is a passion.
Actually a big part of the medical school interview is making sure you are passionate about medicine. You are pretty much expected to be doing some type of medical volunteering on an ongoing basis to demonstrate your passion. In addition, once you are in medical school, interviewing for residency, demonstrating passion by volunteering or leading a journal club is often a big boost to your chances.
* Whiteboards
As part of the USMLE (US Medical License Exam) there is a clinical skills section. You go into a recorded room with a standardized patient who pretends to have a certain illness. You are expected to ask them the right questions and do the correct exam. You are graded on how well you do.
In addition, before you can get board certified in your specialty (especially in surgery) and be allowed to practice on your own without any supervision, you undergo what are called oral exams. It is kind of like whiteboarding. There you are given hypothetical patient cases and are asked to walk through how you would diagnose it. What questions will you ask, what exams would you do, what imaging or other tests would you order. You are also asked about your treatment plan. If you are a surgeon, you will be asked to walk through how you would do the surgery, including what type of incision and the surgical approach. The examiners may throw in some complications (such as a lot of bleeding) and ask how you would deal with it.
In reality, the medical doctor interviews are much more demanding than the software developer interviews.
Source: I am a medical doctor and software developer and have done both the doctor interviews and the whiteboard interviews.