V IS FOR..............

"v" is for RBD and pops.. "vel" is for volumes...

emitting only 1 particle per point per frame

Obviously stole this from ODforce:

if you want just 1 particle emitted per point at a given frame, the basic expression would be in the rate of the source node of your pop network
if you decide to put it in the impulse rate :
npoints(opinputpath("../",0))
and turning off the const. activation
if you decide to put it in the const rate
npoints(opinputpath("../",0))*$FPS
and turning off the impulse activation
don't forget to put the emission type to points(ordered) or you won't have a particle per point
this will hower emit the exact amount of points your emitter sop has per frame, so if your emitter has points that last 2 frames, you'll have 2 particles per point after 2 frames.


*Also, you could use $NPT/10 instead of npoints... Dunno if this works

When would you use this?
If you have a source which is changing point count each frame, eg, a pattern of cracks being animated (like when Godzilla is underneath a road)... 
I think the $FPS version helps when it comes to substeps etc like with Maya, where you need to divide the perframe emission to account for the substeps... 

The first option works well if you divide the emission count (just add a /10 or whatever after the expression)

random rotation with POPs

To get random rotation with POP particles, add a point wrangle at SOP level with a more specific version of the following code-

v@w=rand(x-value,y-value,z-value);

Then in the dop network, add a POP-torque node and set the amount to zero, so that it takes the initial "w" value. "w" is angular velocity..all according to keikaku.