Yorba, the IRS, and tax-exemption

Copyleft licensing would not have changed anything in Yorba's situation; the IRS was concerned that the software could be *used* by for-profit entities, and that's still try with copyleft (and all other FLOSS) licenses.

Also, 501(c)6 is a trade association, which is how the Linux Foundation is organized. It it also what the Open Stack Foundation was applying for. 501(c)4 is for entities that are not primarily composed of (and receiving funding from) businesses.