I've been playing a wonderful little html5 game over the past week called Entanglement. Difficult, yet surprisingly addictive. You have to make a big stringy mess by placing tiles on a board.
I have to say that I am not very good at it at all. But such is life. It works well in Firefox and Chrome. They also have an offline version available for Chrome as part of Chrome's web store. It's free, though. Don't just sit there; go and play it!