The problem with OpenDarwin was that there was little interest in Darwin-proper, turning OpenDarwin into a mere hosting facility for several Mac OS X-related open source projects, which was not what the maintainers had signed up for. OpenDarwin was supposed to increase the cooperation between the Free software community and Apple, allowing both to profit from each other, but according to the project maintainers, the idea of creating a stand-alone Darwin operating system had failed. Remember, this happened during the PPC-Intel transition, a time where Apple refused to release the sources to Darwin for a while.
Last year, the PureDarwin project was founded to continue the effort of creating a stand-alone Darwin operating system. In a relationship similar to that between Debian and Ubuntu, PureDarwin draws from DarwinBuild, adding various Free software components like X.org to create a usable version of Darwin. The "pure" in PureDarwin means that the project does not use any Mac OS X components, sticking to Darwin-specific tools only.
The current developer preview release can boot into X.org, and comes in the form of a VMware Fusion 2.0 image. This release is just a proof-of-concept, to show that "Darwin 9 is alive".