PHP gets websites built. But what use do I have for it if I want to make software? you know, something other than pumping ascii over a socket descriptor?

Careful, that's a form of heresy around these parts.

The kicker for me was discovering that Facebook's PHP shell (http://www.phpsh.org/) is in fact written in Python.

The toolbelt of even the least experienced craftsman has more than a single tool.

Give me an example of something you can't do in PHP. The language is turing complete .. your statement makes no sense.

I think the issue is whether one would even want to attempt to develop certain types of software using languages and environments that were designed to be used in a specific way. PHP would certainly not be one's first choice for developing native Windows desktop applications, for example.

Given the needed supporting technology, you can write a filesystem driver in PHP. With FUSE, you can.

What we should be questioning is how pointless would such endeavor be.

Like kenjackson pointed out (and, oddly, this time I agree with him ;-)), your toolbox should not be restricted to PHP, however Turing-complete it may be.

I wonder if you could write FUSE in PHP...

You would need to extend PHP somehow and make the kernel and its data structures visible.

But I have no intention of even dedicating one minute to such thoughts