A fun game that's easy to learn but difficult to master.
TWIXT Wiki: rules, etc. (http://en.wikipedia.org/wiki/TwixT)
https://www.youtube.com/watch?v=PQ-YB6RJODo
Twixt (http://twixtlive.com/Play.aspx): Play against computer - way too easy, but you can also play against people. I think.
TWIXT Puzzles (http://www.ibiblio.org/twixtpuzzles/)