hi - Language Perfect is great for just vocab activities. Although it was developed in New Zealand for people learning a language other than English, it has expanded for ELL. You can select both the base language and the language being learnt. I teach Indonesian myself, so am not familiar with the English / Spanish content but it is used around the world now.
For designing your own specific sets free of charge, quizlet is populer (not such if there is an app) and cram is fantastic as it has some games that students find pretty cool (including a space shoot 'em up themed spelling game). Again, I don't know if there is an app.
Good luck! Will follow to see what other suggestions you get!