World Music Day is celebrated every year on June 21st with free concerts throughout the city, and around the country. This festival is one of my favourite things about France. This year I went out only briefly, but it was to see my brother-in-law's band Zozophonic Orchestra.
The festival was born in France and has since spread to several European countries. This year it was celebrated in New York City for the first time. You can read more about the history at Wikipedia.