<p>Well, since you didn't get paid, it is not really work. Just be honest, don't play head games with yourself trying to make it look like something it is not, because in the end of the day it doesn't really matter what section of the application it is in, as long as it is on there.</p>
<p>You could list it under work experience as an "unpaid internship" of some sort, or an extracurricular activity. It is really up to you, as long as it doesn't misrepresent what you did.</p>