I'll have to do more reading but it looks like it's contemporary to the Libertarian Communist writers and maybe, hilariously, a parallel attempt to unify anti-statist socialism and communism.

Putting this here mostly to help my memory and have a searchable comment on my history. Proudhon referred to himself as a Mutualist, an Anarchist, and later a Federalist. But not a Libertarian. Left Libertarianism obviously has cause to reach back and claim him but those writers came later, and not as some claim, contemporary with Marx. It is fair to say LL has it's roots in the first international, but it is very much an evolution of left Anarchism, not an origination of left anarchism.