I would say that in job interview context, pretty much all questions implicitly contain “explain why” part. It’s safe to assume that nobody is interested in hearing one-word answers. If - for whatever reason - they really wanted very short answer, the onus is on them to interrupt you and ask follow-up questions.
Now, it’s not clear to me what exactly is this answer supposed to measure. You can probably name something new and trendy at the moment to show that you are keeping track of latest developments. You can probably explain in detail how this particular app is making your life easier. Maybe you can give some example on how team behind the app was helpful and responsive in your support queries. Or you can say that apps are tools, and while you find some of them to be great, at the end of the day the only thing that matters is whether they are getting the job done or not.
Personally, I would probably go with the last option. But I’ve never been asked such question.