Hi, SPH (Smoothed Particle Hydrodynamics) would be a cool thing to add.
This would make the water(rain) or sand look much more realistic.
I was trying to add it by myself, but no chance.
Do you think that is possible?

well yeah, physx provides some builtin fluid systems
I have it on my todo list

Oh, that's cool.
I don't know if this is helping you, but I found a program using SPH and it is opensource.
Iif you think that would help, I will give you the link.

sure, links to good sources are always welcome

<!-- m --><a class="postlink" href="http://www.rchoetzlein.com/eng">http://www.rchoetzlein.com/eng</a><!-- m --> (good site with videos and source codes)