An Excellent Free Graphing Calculator for Your iPad – Desmos
Desmos is a free graphing calculator that originally launched a few years ago as a web app before becoming an iPad app (the web app still works too). Recently, the Desmos iOS app was updated with some good features for students. First, Desmos is now properly formatted to work in landscape and portrait mode on iPads and iPhones. Second, you can now take pictures with the app to insert them into your graphs. Third, and most important to me and first-time uses of the app, a guided tour of the app’s features are now built into the app.
In many cases using Desmos is a good alternative to purchasing expensive TI-84 Plus (or whatever the latest model is) calculators. If your school has a 1:1 program with laptops or iPads you can use Desmos in any classroom.