An efficient mechanism to fund public goods would provide huge benefits to the whole society. There are countless examples where the overall utility of a public good for a group of people would outweigh it's costs by orders of magnitude but nevertheless due to a lack of coordination and the free rider problem the public good doesn't get build.
Because it is easier to finance a private good we turned things like (digital) music, movies, books, ideas into private goods (artificial scarcity) with copywrite and patents laws. Imagine the boost of society if we could come up with a solution the keeps the (monetary) incentives to create such goods but would work for public goods. All digital goods could be free, or to be more specific - usage would be free of additional costs. Please note that also physical goods would become much cheaper - an extreme example is medicine where the marginal costs are often also close to zero compared to the full costs today that also tries to finance the research. Even for a macbook the marginal costs are significantly lower.
So how could such a mechanism look like? The general idea is something similar to Spotify. Every member of society pays in a fixed amount and therefore gets free access to all goods (music). Now the usage of the good is tracked and the producer of the goods gets rewarded from the total money pool proportional. The problem now is - how can we get everyone to agree to pay this tax without the very unrealistic assumption of having a global benevolent Leviathan.
The answer might be to build it into our money system. < insert description of Circles an why it might work>
In a system like Circles a funding mechanism for public goods could be build in in the core mechanism of the monetary system. Whenever new money is issued a percentage of it is set aside to fund public goods. In the concrete idea of Circles that would mean that every person has beside its basic income an amount of money to spend for public goods.
The person should be able to choose what projects they fund but the default option should be that usage is tracked and payed out accordingly. Circles offers an additional mechanism to prevent abuse. An easy abuse of this system could be to fund only a project where you are the author. However - since this fundings are public others could and should stop accepting your personal currency like they should stop accepting your currency if you use multiple accounts per person. For good design decisions the principals of Elinor Ostrom for commons should be used.
If more enforcement is needed digital public goods could develop a licence agreement that grants usage rights to everyone participating in this scheme.