A public platform where anyone could start a crowd-sourcing cause (set a goal, conditions of execution, and dates) then have people contribute money to grow a fund for a specific goal.
I use the term "unsolicited" because, at the time of project creation, the team who will eventually be executing the project has no idea about its existence.
If the fund grows large enough to reach the set threshold and all other creator-defined conditions are met, the project goes for execution.
A team of experts is then assembled to direct and oversee the execution (fund contributors vote in the experts)
The experts then transparently execute on the conditions set by the project creator
If all conditions are not met, the money is refunded to contributors
To get stuff done which otherwise was unlikely to happen or is much overdue.
Create a fund for a specific goal then let entities apply. In a transparent way, let competent experts narrow the applicants to the top 5 most suitable. Then let people who contributed to the fund vote on who of the top 5 gets to execute the project.
Create a fund to have a specific person (obviously Elon) use it on a specific project (obviously radical life extension) to the best of their ability. Should they accept, the money goes for that purpose. If they don’t accept by a certain date in the future, the money goes back to the contributors.
Create a fund to have a specific person/entity use it on a project of their choosing
Examples of such unsolicited crowd-funded projects
people gather a 100 million fund to have Elon use it toward creating, directing and overseeing a transparently run research and development company (much like he did with OpenAI) which aims at radical human life extension
people gather a 5 billion fund to have the most competent team lead the way with the most viable solutions to decarbonize our planet
How to keep the money safe
A trustworthy entity (a long-standing law firm, etc) would keep all the funds in escrow until the conditions for execution or refund have been met. This could also be done on the blockchain (Ethereum) via a decentralized autonomous organization.
How to keep everything transparent
A portion of each project's fund would always go for operating costs. That includes assembling a panel of experts who do everything transparently and publicly. They make sure that all the rules are followed and conditions met.