NSP Program What Exactly is it?

I see a number of listings on the market offered only to owner occupants, City, and charitable organizations for the first 14 days, under the NSP program.  Does anyone know of a link showing the rules and regulations regarding this program?  I would like to know what incentives, if any the seller is receiving. 

It surprises me to think, we are supposed to be the experts in the field, but we know little about the function, goals, and success of the NSP program.  Other than a local city department, providing down payment assistance to first time home buyers, and news releases stating the federal government has released billions of dollars, I can find very little about the NSP program.