As soon as you start paying individual maintainers, it stops being nonprofit OSS they work on. If you direct your funds to other charities, you're only shifting the tax issue to them. If you want to give money to maintainers with no strings attached, it's basically impossible to avoid double taxation.
We explicitly explained to the IRS that our endowment plans to make awards and grants to individual OSS developers and maintainers in the US and other eligible countries. Given our limited target scope — not just any software, but critical nonprofit independent OSS — it was acceptable, and the IRS approved our 501(c)(3) status. And we plan to operate within what is described in our application.
