Masterplan is an adventure planning / campaign design tool for Dungeons & Dragons (4th edition).
It's free, and you can download it here. You do not need a DDI subscription to use Masterplan, but it's generally recommended.
Feedback, feature requests, bug reports, job offers, proposals of marriage all welcome, via email, blog or Facebook. If you find Masterplan useful, please tell everyone you know! If you find it useless, please tell everyone anyway, but lie.