This one is for the iOS series of devices, including iPhones and iPads; the Free Graphing Calculator for iOS. This has a lot of built in functions, solvers for a variety of equation types, constants including those necessary to do orbital mechanics calculations, reference material including some very detailed but understandable explanations of how the various logic gates work, and a whole lot more. If you do anything with math beyond count your change at the checkout counter, this app will help you do it a lot faster and easier. Thanks to the folks at The Daily App for the heads up on this one. If you have a iOS or Android smart device you will want to visit the Daily App once a week or so to check out all the interesting goodies they find.