Another ZPU simulator?  Really?  Yes.

The one in the offical ZPU git repo is written in Java and requires gdb to work
- yet there's no pre-built gdb binary for the ZPU - so getting this up and
running and learning how to use it is going to be more work (and less
educational!) than writing a new simulator from scratch.

The ZPUino simulator has some x86 assembly language in it, so can't be built
on a 64-bit Linux install, and is also tightly coupled to the ZPUino way of
doing things.

The simulator isn't complete yet, but implements enough of the ZPUFlex
variant of the CPU that I've been experimenting with on retroramblings.net
that it's useful.