I'm looking for some good music theory software so I can study & keep up over the summer, before I take a music theory placement test in the fall semester.

Ideally, I'd love something that I can use to review the basics, but also use to practice and learn more advanced material. Reviewing diatonic harmony would be great, but I imagine there's little out there that'll let me do that.

Any recommendations? What music theory software do you like the best?

Thanks!