Oski is played on a field made up of 19 hexagons. The board starts with a three-letter word placed in the center (you can let the app pick one randomly or choose one yourself). From this point on, a turn is composed of a player adding one letter to the board and then using that letter to form a new word. The rules for creating legal words are kind of an aggressive version of Boggle. You can connect letters to their neighbors, but you cannot double back or reuse letters within the same word. Most importantly, once a word is used, you cannot later create a variation of that word. So, "eye" eliminates "eyed," "eyes" and so forth. Also, you cannot make a shorter word that can be found inside a word that was scored earlier. In the example on the right, the computer began the game with the word "cru," which then prevented us from playing "crude" or anything like that.
As anyone who's played Scrabble or Bananagrams or who has done a crossword can tell you, being able to pick your letters is sort of a blessing and a curse. You can make the words you want to make, but this flexibility comes at a price (for players who enjoy a quick game, anyway) because you really need to calculate out all the options with each play. The game is usually decided by a handful of points, like three or four, so even one or two sub-par turns will almost certainly doom you to losing.
Still, there is a good game here with lots of tension, and there has even been an Oski world championship (the app's developer, Richard Malaschitz, participated and came in sixth. Oh, he also created the game itself). You can read more about the game here and here.
The main problem with the app is apparent before you start to play. After all, you need to read the rules to know what you're doing, right? Here, you can easily get lost in nonsense sentences like, "For every move player put one letter on board and found word with this new letter." The good news is that after a few moves, you'll have the rules and interface quirks down and can focus on playing the game instead of the unclear rules.
The rules are also unclear on how to input letters, but this is not impossible to figure out with a little tapping around. If you want to use a letter in the middle of a word, for example, you need spell your word by tapping letters already on the board and then the blank space where the new letter goes. This will call up a window with the alphabet in it (all caps), which you then tap to insert the letter and then continue with your word. This isn't spelled out in the rules, so you're welcome.
The app comes with five dictionaries/languages you can use: English, German, French, Spanish and Slovakian (that last one gives you an indication of the origin of the app, I think). More languages are promised in future updates, too. The dictionaries are not great, missing perfectly legitimate, if unusual, words like pistle. Giving the user the option to override the built-in spellchecker would be very welcome.
The pen and paper version can be played by two players, but one of the main benefits of the app is an AI so that you can practice alone. The computer makes its moves almost instantly (at least, it does on the lower levels), but it never gets mad when you take too long to make your move. There are 50 (!) different levels of AI to play against, and you need to beat one to challenge the next level. Luckily, Level 1 is the feel-good-about-yourself level, where the AI apparently can't build words longer than four letters.
To help keep track of your game's progress, there is an ongoing list of words at the bottom of the screen. Oski also features one of the best undo features of any board game app we've ever played ... because it has redo, too. In fact, at the end of the game, you could back up the game to any previous play, make a different move and see if that would change the outcome of the game.
Right now, Oski feels like a half-done game. Everything works, but there could be more polish. Thankfully, future updates should bring us turn-based online games, global score tables and email and Facebook support. At its core, though, Oski remains a very simple game. It's great to have on the iPad (but why not the iPhone?) but can also easily be played without an iDevice of any kind. If that's what you want to do, go for it. If you think you might play it more often in a digital form or want to support development of interesting apps like this, then head on over to the App Store and tell 'em TUAW sent you.