btCudaBroadphase is some R&D work, a first attempt to use CUDA in Bullet. It uses the NVidia CUDA particle demo grid broadphase as Bullet broadphase. Press 's' to toggle between the original CUDA particle demo and using Bullet+btCudaBroadphase. See some related discussion here: http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=500&start=105