is there something like open source / github type law opinion collaboration: case-in-point being Apple not paying its taxes being about to get out of more than $14 billion with a last appeal needing arguments.

I don't know of such a thing, but if it exists I don't think it should start with the assumption that Apple "got out" of paying taxes in Ireland.

The EU claims taxes are owed to Ireland.

Ireland says no taxes are owed.

Apple says no taxes are owed.

You may disagree with Ireland's tax policy, but that same policy has been an absolute windfall for the Irish economy which is now, on a per capita basis, among the highest in the world. Huge win for a people who were poor and starving less than 200 years ago.