Gratipay (gittip) comes to mind, but that's a donation mechanism, rather than the information collection you're describing. Sounds like a good idea for a project. IMO, the hardest part of that will be accurately prioritizing which projects are critical, very important, moderately important, etc.

Freedom of the Press Foundation does this although they target projects and organizations that focus on issues related to the press and journalism.

Example: https://freedom.press/bundle/encryption-tools-journalists

Here it is: https://www.fsf.org/campaigns/priority-projects. It seems not all of them have clear 'donate' buttons, but donating to fsf with a comment might work.

That could be an interesting project for someone. I suspect the hardest bit would be how you determine which projects are most important or most deserving of donations. As soon as money is involved, people will try to game it and spam it.

I think the package managers should add links to donate to projects. So I open up Synaptic to install GPG and in the description see that I can donate and they're only at 25% of their funding goal.

Another key would be to add a real commercial justification to pay for projects instead of just donating. Often for tax and regulatory purposes businesses can't just spend money on fun, frivolous things unless they want to make a mess of their accounting. Maybe something like for each $50 you spend you get to ask one question on a mailing list or message board.

I think the simplest method would be to consider total amount of donated money.

As in projects that are attracting lots of donations are probably important? Or as in projects that aren't getting many donations probably need more?