Studio Neat on offering their app Slow Fast Slow for free:

When you launch Slow Fast Slow for the first time, you are presented with our “ad” for the Glif. It consists of five screens that you swipe through, showing off the features of the Glif with text and looping videos. A link to to learn more and hopefully consider purchasing the Glif is included towards the end.

Just what I was thinking last week. The app as an ad platform to sell other stuff. If done well, meaning properly placed ads fitting within the theme, this could actually work and create a great new marketing platform.