I'm evaluating Houdini.
I'm looking for documentation, on the $Variables.
Is there a list?
Where do I look?
The help refers to a few like $F where are the rest?

So far looks pretty good.

Paul

Not sure where you are looking, but my help page shows a pretty complete list:
http://localhost:48626/expressions/_globals [localhost]

There's the globals, but there's also a sizable list of local variables too, often common between OPs but nonetheless local - each OP has a help page which you can open with the help icon on the upper right of the OP's parameter pane. There's coverage in there of local vars.

Cheers,

J.C.