NumFOCUS

I’m imagining the same product and support as open source, and basically the same value proposition as a donation (eg no promise to support anything), but coming under a different name that is more inline with university procurement services (eg an invoice for a product).

I hadn't found the university side to be a problem. Gifts seem to work well. Usually the problem is to create a value proposition for the company, in my experience.

Accepting gifts isn’t a problem, the bottleneck is finding the source for the funds. I don’t think I can use my grant money to make a gift to NumFocus. Maybe It’s possible technically (I doubt it), but it’s certainly not something you would normally budget into a grant.

I think I misunderstood your "via federal funding" part, makes more sense now. I never imagined it to come from someone else's funds.

I don’t have any evidence, but “my gut” tells me that there are a reasonable number of PIs that would not hesitate to budget in $500-1000 into a federal grant so that they could “purchase” open source scientific software.

I think one challenge (as @amuellerml pointed out to me) is that many OSS projects aren't structured to know what to do with cash if it came in. There's some organizational R&D to be done there too

One problem is having the project manage and spend funds, the other problem is credit assignment. How do you decide who to give money to?