Donations are very unnatural for for-profit companies, unlike payments for services, requiring a lot of work to prove the legitimacy of a donation.
Furthermore, funding public goods with donations creates ethical issues: in a competitive environment freeloaders have a competitive advantage over donors.
Is there a way to contribute equally and fairly to public goods? Yes: taxation.
The same way it's been done when public money funded all the groundwork for semiconductors and early computers, GPS, GSM, satellites, fiber optics, LCDs, touchscreens, spread spectrum, particle physics, space exploration, industrial chemistry, nuclear power and so on.
You create international projects and hire very skilled people to decide funding allocation and hired skilled people to do the work.
Without the distortions caused by the interests of for-profit companies (or the whims of some billionaire) you have a more efficient innovation process.
DARPA basically pored money into the very bleeding edge of tech, not the day to day stuff. They are interested in innovation because they want smarter weapons.
They essentially funded R&D then left private companies alone to profit from that R&D.
So I don't think that model applies to say a web site analysis tool, or another text editor, or a cutting edge todo list app... You know, the boring OSS software we use everyday...
To be fair, you often end up with the whims of some billionaire replaced by the whims of some bureaucrat. Thus, a key part of any such arrangement is transparency and accountability before the society it's supposed to benefit.
Sure, but even a corrupt and poorly implemented democracy is more transparent and accountable to the public than any private company belonging to said billionaire.
Being removed from the public eye is the whole point of the word "private".
Furthermore, funding public goods with donations creates ethical issues: in a competitive environment freeloaders have a competitive advantage over donors.
Is there a way to contribute equally and fairly to public goods? Yes: taxation.