With Tangoword, you can listen Japanese words like you listen music on your phone. Start the Tangoword and press play, Tangoword will start playing like any other media player and tell you Japanese words and their meanings in English one after the other. This way, just by listening it you can memorize or repeat Japanese words you know. It works on background so you don't need to see the app itself, just start it and put it on background and do whatever you want on your phone.

You can pick difficulty of words between N5 (easy) and N1 (hard) and Tangoword will only give you the words at your level. There are more than 8.000 words grouped by difficulty according to official Japanese proficiency test JLPT. It is also possible to change speed of the app or listening English meanings first and Japanese words later.

Lastly, it is completely free, no ads or anything like that. That is nice.