Want an idea that's interesting, pretty easy to start off with, and has opportunities to do be extended?
Make one of these for Pygame: http://lab.andre-michelle.com/pulsate Bonus small-time money-making opportunity: Make an Android app and let me know where my friends can purchase it. Note: I believe that game mechanics are not subject to copyright/trademark, so I do not think this is legally stealing someone else's idea. If you do, I apologize. I don't want to incite bad behavior.
