Summer time in the United States generally means people have a lot more free time to enjoy the outdoors. The sun is out for longer, so there are more hours in the day to enjoy. Having more free time does not mean you need to spend a lot of money. There are plenty of ways to enjoy your city or town for little or no money.
In the summer, many parks offer free concerts. Sometimes these concerts feature bands and musicians that are well known. Other times the concerts are given by up and coming artists. Regardless of whether you know the band playing or not, these free concerts in the park are a great way to enjoy music outdoors. If you arrive at the park early with your friends, you can even have a picnic.
Many parks also offer free outdoor screenings of movies. It's always a good idea to arrive early to get a good viewing spot. Being too close to the movie screen is no fun; your neck will hurt. Sitting too far means you'll have to squint. These outdoor movie screenings are also great for picnics.
If theater is more of your thing, most major cities have some Shakespeare-in-the-park programs. These programs feature different works of Shakespeare performed live and outdoors. Many of these programs are free. Some of these Shakespeare-in-the-park programs are so popular that people line up for hours to get free tickets. Usually the tickets are first come, first serve. If all the tickets run out before you get to the front of the line, then you are out of luck. So get there early!
If you don't have air conditioning, many museums offer free admission days or hours. Besides the museums being cool temperature wise, they are also cool because you can see amazing works of art.