Yes, I kinda attempted to keep it vague. As of this moment, I'm transitioning into management (or so have been the last month), and I need something to keep me entertained...
Using C#/Java, maybe some front-end stuff would be ideal. Or possibly getting into Ruby/RoR.
I utilize the Startup Weekend as a tool to work on stuff and do something fun. Check out the upcoming events at: http://startupweekend.org/events/
I haven't found a website that keeps track of Hackathons...