The Ioun Stone

[leegi0n]

Just out of simple curiousity....

Is there any restriction on who or what can own/use one of these good ol' gems?

[faceroll]

They are the quintessential slotless item, so anyone can use one. Of course, if it's command word activated, you're going to need a mind to decide to say the command word and a method to vocalize.

[Gnaeus]

Well, you have to hold it and release it, so some manner of manipulator is probably required (hand, tentacle, maybe paws, you could hold it in your mouth, etc, but a slug for example couldn't do it).

And it orbits your head, so you may need a head.