I knew before I even clicked on the link that they would describe it as "Sudoku with letters," and sure enough, those were the first words of the description.
The only problem is that, other than their shape, they really aren't like sudoku at all. There's a completely different skill set involved in creating a word square and solving a sudoku. (And, since I haven't said so on this blog yet, I might as well say it now: I don't like sudoku, and I'm frankly baffled by its success. The idea that they're replacing crossword puzzles as the favorite puzzle pastime is simply further proof of the decline of Western Civilization. But I digress.)
Imangi's Word Squares is a nice little puzzler with 20 sample puzzles in the free version, and 1,000 in the $2 version. These aren't the kind of pure word squares about which I wrote yesterday: the vertical and horizontal words are different. This actually makes them easier to build but harder to solve, since finding 1 vertical word does not mean automatically finding 1 horizontal word.
The puzzles themselves range from 3x3 to 6x6, with the 6x6 providing quite a nice challenge. This is far more difficult to do than sudoku, since you're not merely finding the proper placement of each letter, but also creating actual words.
The squares are quite easy to use. There are white letters and black letters. The white letters are fixed in their proper place, while the black letters are moved to form words. This is done simply by tapping two letters to exchange their place. If you get stuck, there's even a hint system that moves one letter to its correct place.
There's quite a lot of puzzle play time in this app. Try the free version to see what you think.