Let's build an app!
I have an itch that an app can scratch. When I'm getting ready to leave the house, I'd like to know how much outerwear I need and whether I should bring an umbrella. I could look up a weather forecast online and from that extrapolate what I need to wear, but it would be much simpler if I had an app that just told me what to wear. This app is Sweater.
One way to use Sweater would be to access it on my mobile device. Another is to have it up 24/7 on a dedicated device close to, say, my closet.
Herein, I describe both the design process a design process that gives us a good design spec for building the app as well as at least one way of implementing it.