Have you applied Game Theory on a project? -

I have not read, but it fascinates me that my intuition is that most of it is not used by "enterprise app" developers However, it is clearly relevant for large online sites (example recommendation systems), and there is a huge impact on SO.

Have you implemented any theory of game theory in your daily projects? If so, then what principle?

I'm sure that Google should have a strong taste of the game theory to work on auctions on Google. , Or at least micro economics of judgment under uncertainty ...