Years ago, I needed to parse and view custom logs from our proprietary app, and I needed to do it now, so I cranked out a little Ruby script. But then I needed to share it with a non-programmer... so moments later, I slapped on a little Shoes GUI and it was good to go.

I believe the same tool is in use even now, over 10 years later.

Probably the fastest script-to-GUI iteration I've ever done, and a good showcase of Shoes' simplicity. (Although, the GTK gem is actually pretty easy to use as well, and my most recent conversions have been with GTK.)