it is still under development. Here is the link to actual source code:
https://www.gitorious.org/blenderprojects/blender-lukastoenne/trees/particle_nodes
Lukas said, that:“Loads of uncommitted stuff here, will push this once i get all the nodes back up (as far as they’re still used). Basically the whole emitter and object interaction system will change. That was one of the weak design points”