Crossy Word

Improve your vocabulary by finding words that can be built from a given set of English letters. Any words you find go into the crossword puzzle, or add up as extra words which you can then trade in for hints. There are 700 levels in the game of increasing difficulty, with more letters to build words from, and bigger crossword puzzles. The app is completely free, doesn't have in-app purchases. You can watch an ad for extra hints.