Games with a purpose

"Each year, people around the world spend billions of hours playing computer games. What if all this time and energy could be channeled into useful work? What if people playing computer games could, without consciously doing so, simultaneously solve large-scale problems?"
So begins Luis von Ahn in his paper on Games with a purpose
Just brilliant - making data-tagging fun, intrinsically.
See Peekaboom, for instance:
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