I am asked this question many times in the interviews. I get confused about which project to tell them and why some project would look challenging or non-challenging. What are they looking for in the answer? Any software is a challenge before it gets started and it becomes a normal software engineering task after it has finished. All softwares I made were challenging until they got finished. Do I misunderstood the word "challenge"? Whats wrong in my thinking? What was your most challenging project and why you think so?