Augmented Reality (AR) Programming for High School?

I am wondering if anyone knows of a good site or app to help students learn about and begin programming augmented reality content.

I’ve seen a number of sites for elementary students which require little or no programming. I am looking for something supplemental (maybe a week or two) for the end of the year, after our curriculum has ended.

I’d prefer phone or Chrome based projects (and free, if possible, because I doubt I could even get anything purchased by the end of this school year). Does such a thing exist?