Another difference might be that most image-based Common Lisp implementations don't use portable byte-code. Some are using byte-code engines, but those are usually not portable across operating systems and/or machine architectures.
But, about the GUI, I was thinking about Morphic. It's basically a GUI designer on its own: you can create widgets by instantiating their objects in Playground. It doesn't matter what widget it is: you can create a button or a list item or a textarea on their own. You can then edit them with halo actions or in the inspector until they look like you want, then add them to container widgets, then finally put them in a window. It's bottom-up programming for GUIs! You need to manually track the changes you make via inspector (ie. to copy them to playground), but if you do, you can copy the whole playground into a method and done, you've just designed a GUI app! You later replace some Widgets with their subclasses written by you to handle events and you're done.
This is indeed similar to Common Lisp and Emacs.
Back to the original question: the VM runs on Windows/Mac/Linux and on some IoT devices. The code is compiled to bytecode which can then be JIT compiled further on some architectures/OSes. The compiler and the whole infrastructure is exposed and available on runtime.
Pharo has classes for easy FFI to C and for bundling native libraries. I don't know if it's possible to call back from C to Pharo, but I assume yes (many libraries require this). There is no FFI or other integration with any other language (at least as a built-in, there are RPC interfaces for some langs as add-on packages).
As for "standalone binaries" - almost, as you need to bundle the VM with the image; there are some helper scripts for bundling and then launching images.
The most obvious use case is GUI programming, there's also old-school Web programming with Seaside, data crunching and visualization with Roassal. Other than these killer-apps, Pharo is just as capable as any other high-level language, although with a much smaller selection of libraries available.