I updated an experiment I did some years ago, you can check it out at www.giroffel.com.
Don't bother if you're using anything below Internet Explorer 9, it won't work as it should. However, you should be fine using IE9, IE10, Firefox, Chrome, Safari ... It also works fine with an iPad or iPhone.
Please leave a comment if you have any suggestions!
PS: I need to change my easy/medium/hard evaluation algorithm of the puzzles, easy puzzles are sometimes too hard and vice versa.