Being something of a writer, I've always been fascinated by word games and love the challenge of having to plunder my internal dictionary to win. Though I'm invariable pretty rubbish at them, these type of games provide a great way of maintaining a decent vocabulary.
Codex is one of the better word games I've seen for the Palm, offering unique gameplay that will keep you coming back for more and more. The object of the game is to form words using the different letters on the game board. As in Scrabble, the number of points you get depends on the length and difficulty of the word.
Playing the game is simple enough, and essentially all you need to do is to swap tiles by tapping them. Of course, doing well at Codex is another story because there are more than 500 different puzzles of increasing difficulty to get through.
Luckily, you're not completely on your own, as the game includes a built-in word finder and word list browser, containing over 30,000 words. I thought that the inclusion of a live demonstration was another nice touch.
Unlike some word games this one has legs (not literally, obviously) and will keep you coming back for some time. You can play against your friends to challenge the high scores and Codex lets you save up to ten games so you can carrry on where you left off at any time. Another great thing is that it doesn't force you to restart the game if you lose at one puzzle. You're simply docked points and must start that level again.
It would be nice to see some other language databases in here aside from English, but on the whole, Codex is a great way of bolstering your brain using your Palm device.