Whether you're on unemployment, a homeschooler, staying home while you heal, or you're kids are staying home because their schools are shut down from swine flu, the best use of free time right now is to learn more (the distraction from boredom and stress may also be more important than you realize).
There are many more online. If you have a specialty that isn't covered here, unions, trade associations/research centers, etc. might have special programs (investigate).