Bancor is a protocol for token exchange, which is based on a new model where the price discovery is not based on the agreement between two parties, rather, it is based on an equilibrium-seeking model in which every purchase of a token increases its price, and every sale of a token decreases it. The price equilibrium point is the price-point in which the amount of buys and sales of the token are balanced. You can read more in our draft whitepaper (link)