Weaver Unlimited is a fun option for those looking for a challenging word game. The game has gameplay quite different from many current word games.
Specifically, you will use the two 4-letter words provided to build a word ladder. You must start with the first word and follow the rule that the following word must have only one letter different from the previous one. Go on that until you end it with the second word. The game doesn't sound difficult but the real challenge only begins when you actually play.