NASA holds a plethora of knowledge, so much so that it is difficult to consume. To help spread the wealth, NASA has created dozens of free Apps with a wide range of content. You can collect space junk with Space Junk Sammy; and if you are totally into the sun, you can receive notifications of solar flares and see digital 3D reconstructions with 3D Sun. If the Space Shuttle Mission grabbed your attention for 30 years, you can get the 30 Year Shuttlebook and look back at all its accomplishments and innovations. My personal favorite is the NASA Earth As Art app, with gorgeous images of the Earth collected by NASA satellites and beautifully illustrated. You can access the full list of apps here.