Khan Academy

The Khan Academy is a website that offers a free online collection of more than 3,100 video lectures created to support learning .  The Academy started when Salman Khan began remotely tutoring one of his cousins using Yahoo Doodle images. Eventually , Khan transitioned to making YouTube video tutorials.  "We're a not-for-profit with the goal of changing education for the better by providing a free world-class education to anyone anywhere"

And this makes it a good resource for some of our learners with special needs who are visual learners and those who choose to home school their children.  

To learn more about the academy - check out their website.
And yes, there is an app for that.  Check that out iOS app here and what is available in the Android market here.