Some awesome ideas of productivity and software. Or rather, of excess work being harvested. Number one is captcha. Number two is duolingo.
Captcha digitizes books, while providing anti-robot security.
Duolingo provides translations, while teaching people english.
Both use unique marketplace efforts where one side has large buyers (security-needing sites, libraries, translation-needing publishers) and the other side aggregates many many humans.
Usually the Turk services are pure marketplaces. Little aggregation.
So think of this other excess work: gameplay.
Some group X of publishers make 80% of games. And games all require fun and also work by users.
Somewhere in there is some horizontal work service that many gamemakers would like to use.
And if that work can be conceived as a productive task, it can be free for game makers.
Hmm. What is it?