I've recently gotten excited about crosswords. I occationally challenge myself to try to build something in a single flight, without using the internet, documentation, or downloadable packages. It's a fun way to stay sharp and force myself to dig a little deeper into language features. I recently tried to build a crossword editor on a flight home to NYC from my parents' house in Nevada (just over 4 hours).
It does stuff like apply the symmetry rules automatically, which is fun I guess. If I wind up using it I'll finish the sharing feature, which I think is the most glaringly missing feature. Use a dot to fill in a square.
Be careful when resizing, it completely wipes the board.