That looks very cool. http://github.com/enjalot/EnjaParticles
only mentions Android, or does it also work on Windows?
Yes, we are experimenting with GPU acceleration of Bullet through OpenCL cross-platform and DirectCompute. There is some OpenCL work in two branches (OpenCL and AmdGpuCloth), and we plan to move things to the trunk/public release.
We are also working on OgreKit: a cross-platform open source standalone replacement of BGE, using Ogre and Bullet, that can load .blend files. It also uses CMake as build system.
It might be fun to integrate your OpenCL particles in there too. See http://gamekit.googlecode.com