Came across this last night. The short story is the author recently had his brother pass away. One of the items in the will was to go to for pizza and leave $500 tip to a waiter or waitress. Full story here http://aaroncollins.org/?p=13.
Below is a video showing what happened when they did this.
They have now received enough donations to do this each week for a year. You can find more on this at the website http://aaroncollins.org/