Unless you are talking about a different Paper, Paper was a free app with an in-app purchase of tools (different brushes) available.

I know this because I downloaded it because it was free and then bought the tools. I wouldn't have tried it if they wanted the (I think) $4.99 up-front.

Good example definitely. I wonder what kind of money they're making. I also wonder if they would be able to do the same thing in 2014 that they did a few years back when they launched. I perceive the landscape as far more competitive, but I could be wrong.

Sometimes ... just sometimes, a fantastic product, and good lifestyle-type marketing (at least, from the videos on their site) can make all the difference. Paper is just leaps and bounds better than any other similar app ;)