To help me learn HTML5, I decided to combine it with a passion of mine — crossword puzzles. The result was a pure HTML/JS/CSS interactive crossword puzzle. I’ve since ported this to a mobile app for android and iOS using cordova. (The source code is not available for the public.)
You can view it in full screen here.
Use the arrow keys or mouse to navigate, then type in the letters. Use backspace to delete characters. Space rotates across and down. Tab and shift-tab go to the next and previous clue. Hit enter to put multiple letters in a box.
The grid is an HTML5 canvas drawn via javascript. Your entries are kept in local storage and re-populated when you reload the page. I used jQuery to help with many aspects of the input and drawing.