Description: Features-loaded encyclopedia which gives you short, quick and relevant search results. I find it most useful for solving complex math tasks such as calculating matrices, derivations, integrals and differential equation. This really helped me in my first year of college (got an B in math 1 and A in math 2), so I reccomend it to everyone who needs a bit help in math, or just simply for checking their results!
UPDATE: This is not android-only app, you can access Wolfram's knowledge engine via your PC, which I also strongly recommend! You can also take quick tour to see what is this engine all about!