Just a quick post to show off what I've been working on recently.
I haven't had time to write up a single shred of documentation yet and the reason I'm posting this in this state is to get an idea on what developers want and so the more advanced people can have a play with it.
All the natives map to corresponding functions in vphysics_interface.h from the HL2SDK, these are different for each game. So if you want to see what Valve have to say about a functions (there are only comments for a few though), grab the version of this file from the SDK for the engine you are using and have a read.