Wolfram Alpha was worth the 3 dollars I paid for it for entertainment value alone, but also in case I care to factor a large integer, solve a differential equation and the like .
It's a little hit and miss how to phrase requests ( but cool when it works, see below) and basically is a computation engine in the cloud, but it is convenient and has several keyboards.
Also it has other party tricks like distances, runway data, and traveling salesman between airports "FLL JFK ORD SFO MIA" or comparisons of population area etc between entities "Israel Jamaica Vertmont Palm Beach County"
So it could probably do more than I do with it.