Billions of hours are spent playing solitaire in a year.
By comparison: Digging the panama canal took only as much as work as an average day of Solitaire playing.
I'm thinking, let's use this to make subtitles in various languages
for (educational) videos. We could also use them to train neural
networks or other supervised machine learning algorithms (such as
training systems to correctly classify). You could have it focus on low
confidence estimantes of algorithms.
Perhaps we could make a game of helping people find answers?