There are numerous smartphone apps that can be of use to ESL students and teachers alike.  Here are a few that I have found to be particularly useful.

 

1. Oxford Advanced English Dictionary, Oxford University Press

Instead of carrying around a 1.5-1.7kg book you can replace it with this handy smartphone app. Entries can be bookmarked or you can copy/paste it to an editor.  It comes with audio samples for all words in both British and North American accents.  You can also download example sentences in both accents but they will take up about 430M for each accent.

It's a bit more expensive than the paperback version but considerably cheaper than the hardcover.

Screenshot OALD

googleplay     appleappstore

 

2. Practical English Usage, Oxford University Press

The quintessential and invaluable grammar reference by Michael Swan is now in it's most convenient format ever.  Instead of dragging around a 1kg book (more for the hardcover) you can have the entire PEU reference on your phone or table.  It is fully searchable and entries can be bookmarked, emailed and copy/pasted into your favourite editor.  For teachers and intermediate and above students this is a must have app.

Like the Oxford Advanced English Dictionary it's a bit more expensive than the paperback version but considerably cheaper than the hardcover.

Screenshot PEU

googleplay     appleappstore

 

3. Sounds of Speech, University of Iowa

As a teacher one of the hardest things to explain to students is how to make sounds that are not in the students first language.  It is particularly challenging to describe the mechanics inside the mouth.  The phrase "a picture is worth a thousand words" has never been more appropriate.  This app shows and animated cutaway of the mouth that shows exactly what is happening inside the mouth to produce each sound.  It even has an annotated mode where you can walk through each step required to make the sound.

At a cost of around $3 it's a no brainer.

Screenshot SOS

googleplay     appleappstore

 

4. Crosswords, Stand Alone, Inc.

This is an excellent app for intermediate and above ESL students wanting to increase their reading and vocabulary skills, particularly idioms.  For $10 you can download multiple North American and British crosswords a day in various levels of difficulty from "very easy" to "amazingly hard".  You can also purchase crossword bundles ranging in price from $1 to $8.

There is also a free light version that you can try.

Screenshot Crossword

googleplay     appleappstore