Browse and watch videos from Khan Academy: www.khanacademy.org - the best collection of educational videos covering almost everything (math, physics, chemistry and more).

Features (really very few basic ones):

- browse videos by categories
- download and watch a single video offline or on youtube
- download all videos by selected the playlist and Menu options (depending on the playlist may take a while, so use wifi or good data plan)

Note: this is unofficial application - not endorsed by Khan Academy. I made it for myself so I can watch videos offline when I don't have a good connection and accessing www.khanacademy.org somewhat difficult.