In a World Of Words

The app provides three main modes of play:

Arena (player v player)
Adventure (player v computer with theme bonuses)
Challenge (player v computer, with rules similar to Scrabble)

Within these are a variety of ways to play.
Adventure mode provides a variety of "worlds" that relate to various themes. There are worlds of animals, astronomy, finance, and transportation, with more planned. The key here is that when the player plays a word relating to that theme, they get a special bonus. Proper nouns are also allowed in the astronomy world.