Planner9 is an open-source distributed HTN task planner developed by Stéphane Magnenat and Martin Voelkle.
To know more about it, read the associated paper.
Planner9 uses CMake. It requires the libboost and libboost-thread libraries, and, for the distributed version, Qt4.
You can run a test program, implementing the example of the paper, with:
programs/p9simple
You can see the threaded version of the planner in action with:
programs/p9threaded
The distributed version example is not documented yet.