I had the idea that a plugin from one VM could be dragged into another 
VM's directory and that it could be used just by starting up the image. 
I've done a little experimenting and it seems more of an idea of a 
reality. The functionality is there, but VM developers over the years 
have not seen this as a priority. Typically plugins and their VMs are 
compiled together. Or a person adds one by recompiling a VM compilation 
rig they already have.

As I had a rig for the Interpreter VM I decided to compile a plugin and 
see if I could drag it around to other VM directories for use. Most 
times it didn't work.

I compiled a TheUniversalAnswer plugin which returns 42. I moved it from 
a 4.14.1-3430 VM to a 4.14.1-3414 VM. I could get it to work if I did 
not use the squeak.sh start script. That is, I dragged so.vm-sound-null, 
so.TheUniversalAnswer and so.vm-display-X11 into the same directory as 
the VM binary. That worked.

The only way to see the external plugins is with #listLoadedModules. 
But, irritatingly, modules are loaded as needed, so once you have proof 
of using the primitive from the plugin, yea, it will appear as a result 
of that Smalltalk listLoadedModules message. So, it's not that useful.

I dragged so.TheUniversalAnswer around to other VMs such as 4.0.3-2202 
and 4.13.10-3268 without success. And the unload selectors 
#forgetModule: and unloadModule:, which both use primitive 571 don't 
appear to work on my Ubuntu 15.04.

So, I don't know if a community of plugins passed around is in the 
offing. What I have learned is that many of the answers are in 
sqUnixExternalPrims.c. The issues are really where does the VM look for 
primitives and what does it do when it finds one. It appears to me, 
after reading both the non-Cog and Cog versions of that file, that this 
an interesting area poorly documented that VM developers alter in haste 
to get on to something else.

It's pretty important stuff, though. Do you start the VM with the binary 
on the path? Do you use squeak.sh? Where is the VM looking for stuff. 
Where will FFI look for stuff. And so on.

Chris

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