On: The Basque Country’s Mondragón Corporation is the ...

[pineaux]

This is the answer to all the above. These shares give you a right to part of the profit, but cannot be sold.

[sokoloff → pineaux]

What does it mean to own something that you cannot sell/assign?

That sounds like plain old profit sharing, not ownership.

[dbingham → sokoloff]

Ownership in the sense of governance, not of property.

Worker cooperatives are organizations that are governed by their workers for their workers, not owned as property to be traded or sold.