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I absolutely love the NS app. It's just perfect: fast, simple interface, accurate information, lots of extra details are included too (tariffs, how crowded the train is expected to be, average delay for that train on other days).
The NMBS should stop wasting money on their own app and get a licence on that instead. I'm really waiting for the day that the NS integrates NMBS live information in their app (which they might as NS International is merged back in NS as NS Reizigers).
In addition to what others have said, you can also get the NS Reisplanner Xtra app on your phone. It comes in English and will allow you to plan journeys, check platforms and train times and give you updates in case there are delays.
Almost all trains and train stations have wifi, so it really helps you get around.
If you need any other forms of public transportation in the Netherlands (trams, metro, busses), you can use 9292ov.nl.
This is the official app for the planning of train commutes (my link appears to be for android, look for 'NS Reisplanner Xtra') you can change the language to English. The word for settings is 'instellingen'.