Its worth to mention it depends on what content you want to protect. If you want to protect content that you yourself own, and the damages if content leaks is not devastating, then you could for example look in the previously mentioned Open IPMP. Suns DReaM project is still availible online, it is however worth to notice that the project is closed due to inactivity. A problem arises when you want to protect content that you dont own. It is very possible that the content owners will not allow their content to be protected by an open source drm solution. Content owners tend to go with proprietary solutions like Microsoft WMDRM/PlayReady, Marlin or Helix. So if your framework will be used to sell for example Hollywood content, I would not recommend putting time in an open source drm solution.
