iSpell is a foreign language vocabulary trainer that utilize well known method of active learning. The foundation of the method of active learning is a creation of cognitive link between foreign and native words and fortifying this link using unrelated to cognitive process activity - a game. The game, spelling trainer in this example, is the active element and nothing more, i.e. ultimate goal is not to learn how to spell foreign words properly (which is a great target all in itself), rather the goal is to create a cognitive link between foreign and native words, i.e. learn foreign words.
By itself the game is pretty simple - for a word displayed in your native language (Español, English, Русский, Deutsch, Français, Italiano to name a few) and pronounced in German you need to slide lettered tiles with your finger to come up with right German spelling. Spoken out foreign word against written native word creates a cognitive link, while spelling activity reinforces the link. Thanks to the method of active learning the process in several times more efficient then passive learning like flipping flash cards and so on.
Viel Glück!