iOS: Khan Academy is a great way to learn about everything ranging from maths to history. Its iOS app has updated to support the iPhone alongside the previously released iPad app.
The iPhone version is rather barebones and only allows you to watch videos. This means you can’t save videos for offline viewing or track your progress like you can in the iPad app or the browser version. But it’s still a good way to quickly catch a lecture on the go, or to learn something new on a long car ride.