I have built a new expression: Snap2Ground.
Its purpose is to stick objects to the surface of another object. Some of you will think, that's exactly what the great OBAN expression does, but mine is different: First of all, you don't need ThinkingParticles. Instead of getting lot's of instances, you simply put objects which should be snapped in a group. Then you can move them around on the surface with the move tool.
Offset from surface and heading can be altered. In addition to this, you can apply some chaos to the objects by varying their rotation and scaling.
All in all, it's a good tool for placing objects (e.g. like stones, trees, cars etc) on the ground.
There's no manual, but since there are only few parameters, you'll get it :)