The Wolfram Alpha Course Assistant apps (iPhone/iPad) and standard Wolfram Alpha for Mobile (iPhone/iPad/Android/Kindle Fire/Nook).
Prices: Between US$1.99 to US$4.99
Despite the differing prices of Wolfram Alpha's apps, nearly everyone that has bought one of its products and shared experiences online has said the same thing: it's worth it. When maths, science or music theory teachers and textbooks aren't enough, and all hope seems lost, Wolfram has the answer. If you're unsure about the price, go to the original Wolfram Alpha website (it's free), and ask any question. If you're unsatisfied with the result, you've either asked a question with an unpleasant connotation, or you're too clever for this world. The app's input system and data representation more or less mirror that of the website; it's a good way to find just the right program for you.
For details go to http://products.wolframalpha.com/mobile
Yes, it helps you organise your homework! You can enter assignments, info on subject choices (useful for remembering new teachers' names and classroom numbers) and reading lists. Each piece of data you add is time sensitive, with resulting reminders at pre-programed times. It's an easy-to-use, no-frills, good-value app. If your school uses an overall grading system, such as the GPA system, you can enter marks for each piece of work: iHomework works out the overall grade - great to see if you're meeting your academic targets.
For details go to http://ihomework.element84.com/iOS.html
AccelaStudy "Essentials" series (iPhone/iPad)
Available for the study of 17different languages, this foreign language vocabulary app has everything from flashcards to quizzes, to sound files of native speakers saying words as they're meant to be pronounced. One useful function is its statistics section, which allows users to find out how they've done on each test they've taken. Another useful revision feature is the app's ability to bring flashcards only after a set interval - say two days (you can decide the time). The AccelaStudy website says 2,100 foreign-language words are included in each version of the app.
For details go to www.accelastudy.com
PocketCAS Lite Free (iPhone/iPad)
The free alternative to the Wolfram Alpha mathematical apps, it can do pretty much anything you want it to, from graphing complicated equations to doing simple arithmetic.
The app's layout takes a bit of time to get used to, but once you have mastered it, you'll have an array of mathematical tools at your disposal.
There is also a paid-for, more extensive version of this app, which costs US$19.99. This version is advertised as being a replacement for graphic calculators at a fraction of the price.
Yet don't use this phone app during tests, though - you don't want be accused of texting other people the answers!
For details go to http://pocketcas.com
This app is pretty much self-explanatory. You can download sets of flashcards online, or create personalised ones, on any subject. It's easy to make new flashcards and bring up old ones: it's perfect for quick study breaks (on the train, bus, during a free period, etc). Armed with this app, pop quizzes and more serious exams should no longer be a problem: if you use the flashcards to revise thoroughly, the information on them will be stored in both your short and long-term memory.
Evernote (iPhone/iPad/Android/Blackberry/Windows Phone 7/Mac OS X/Windows/Safari/Chrome/Firefox)
Take snapshots of anything you like (provided your device has a camera), record a verbal memento, or jot down a simple note as a reminder or list. You can share the note, whatever its form, on Twitter and Facebook, with an option to attach extra files (pictures, documents etc)
You can group notes in a 'Notebook', which makes categorisation easy. Provided you have an internet connection, the app will automatically store a copy of your notes in the Evernote cloud network. .
For details go to http://evernote.com