Double-down's documentation can be found here.

double-down is a double precision interface to Embree via the Mesh Oriented dAtaBase (MOAB). Geometric primitives (triangle elements) are stored in MOAB. Custom primitive types are defined using Embree's user geometry interface where they interface with the MOAB instance to provide robust bounding values for the triangles as well as double precision intersection methods. Ray values come in and out of the interface in double precision, making them useful for scientific purposes while applying the speed provided by the dedicated team of Intel developers who have created Embree.

Assuming you have MOAB and Embree installed already then the installation for double-down would be:

git clone https://github.com/pshriwise/double-down.git
cd double-down
mkdir build
cd build
cmake .. -DMOAB_DIR=/MOAB \
         -DCMAKE_INSTALL_PREFIX=.. \
         -DEMBREE_DIR=/embree
make
make install

double-down is currently underdevelopment targeting Embree Version 3.6.1.