I caught up with the super-smart Richard Sedley yesterday and he pointed me at this astounding TEDx talk by Luis Von Ahn, who was one of the people that invented the CAPTCHA. Luis talks about reCAPTCHA, the project to create human gain from the 200 million CAPTCHAs that are solved by humans around the world every day and apply all those millions of tiny actions towards helping to digitise old books (apparently over 10% of humanity have so far helped digitise human knowledge).
As if that weren't amazing enough, he then goes on to explain his subsequent work to create a product in which millions of online users around the world work together to translate the internet as they learn a new langauge. For free.
What's so fascinating about these ideas are the models and economics they are based on. The indirect but not insignificant benefit that can come from millions of actions from millions of people at a scale uniquely enabled by the internet. Fascinating.