What colleges or places offer free summer programs that are good to put on applications?
You might want check at this Forum: Summer Programs - College Confidential Forums
Check financial aid policies.
I would not attend a summer program just to enhance admissions chances. You do not say what kind of program you are interested in, but I am assuming academic, not music, art or dance. There are many other things you could do, including work or volunteering. Sometimes a break from academics can be refreshing, and you can read freely as well.
What exactly are you looking for?
My suggestion is to find a program that is of interest to your student…not something you think will enhance college applications.