WolframAlpha

Price:  $2.99

Purpose/Capabilities: 

WolframAlpha is a reference app that allows its users to look up different concepts in mathematics, statistics and data analysis, physics, chemistry, materials, engineering, astronomy, earth science, life science, computational science, units and measures, dates and times, weather, places and geography, people and history, culture and media, music, words and linguistics, sports and games, colors, money and finance, socioeconomic data, health and medicine, food and nutrition, education, organizations, transportation, technological world, and web and computer systems (so basically everything!).  It is based off the free website with the same name. 

Not only can you get information about all these different concepts, but Wolfram can also perform complicated computations (including finding derivatives and integrals for a Calculus class) with the steps to go along with it.  It can graph different functions in 2D as well as three dimensional graphs and inequalities, which most graphing calculator apps cannot do.

Results from searching "exponential functions".

Positive Aspects: 

Unlike the free website and many other search engine sites, the WolframAlpha app does not have ads.  It is very user friendly; you simply type in a term or question you want to look up or type in a function to graph or equation to solve.  Wolfram Alpha is a great, reliable source for students to look up information, check their answers, or get help when they are stuck on a homework problem.  It has specialized keyboards to type in math functions. 

Negative Aspects: 

The WolframAlpha app does require the internet in order to use, so if an entire class is using it at once, it can become slow.  As previously stated, the app costs $2.99, whereas the website is free.  The app is considered to be quicker and easier to use than the site.