I enjoyed the Snap courses available in OpenSap, they are all free.
bh posted some recommendations recently after I asked that I was looking for something to do after finishing the OpenSap courses:
Edit:
Found this free PDF by an organization called Code Club , offers free courses. It's for Scratch, but as far as I know, Snap can be used as well.
Edit 2:
Found that Code Club offers the same PDF as a self-guided online course (Link).
hope that helps!