Start with the one nobody tells Marin students about: you can take actual College of Marin classes, for free, while you're still in high school. After that, the open courseware from MIT, Harvard, Stanford, and Berkeley is worth your time too.
Everything else on this page teaches you something. This one puts credit on a real college transcript. College of Marin's College Credit Program, called Jumpstart, lets high school students enroll at no cost per unit. You earn college credit toward a degree, or use it to test out whether a field actually interests you before committing to a major.
Late afternoon classes are scheduled specifically to work around a high school day, at the Kentfield and Indian Valley campuses. Unlike an AP course, where credit depends on one exam score, a college course transfers as long as you pass it.
Two things worth knowing. Students below 9th grade can be admitted with a recommendation from their school principal, so this is not strictly a high school program. And this is real college work that goes on a permanent transcript, so take one class first and see how it fits before you load up.
College of Marin Jumpstart →Here's what I've learned: listing courses on an application doesn't impress anyone. What matters is what you did with what you learned. One course, done deeply, with a real project at the end, is worth more than ten certificates sitting in a folder.