It was a "no-brainer", said eBay founder Pierre Omidyar in 2003, when he decided to reject the traditional model of US philanthropy and stop using a charitable foundation for his giving. There would be an extra tax bill of $1m or $2m a year, but in the context of spending $100m annually on good works, that seemed a small price to pay for what, years later, he called "the flexibility to use every possible tool to improve the world".
Charitable foundations have been the bedrock structure for conducting philanthropy at scale in the US for more than a century. Some of the value of gifts to a personal foundation can be offset against other taxes, and in return, the government requires that the organisations disperse at least 5 per cent of their assets each year and sets other rules, including a ban on political activity.
The eBay founder's decision to conduct his philanthropy through the Omidyar Network, a limited liability company without tax privileges but without restrictions, has been followed by the likes of Laurene Powell Jobs, widow of Steve Jobs, and now by Mr Zuckerberg.
Grants have accounted for only about half the LLC's $890m of spending since inception, says Matt Bannick, managing partner at the Omidyar Network. Its for-profit "impact investments" go alongside, fitting Mr Omidyar's aims of promoting financial inclusion and access to the internet; they include Paga, a mobile phone-based money transfer service in Nigeria and eCurrency Mint, a Dublin company that allows central banks to create digital currencies similar to bitcoin.
"How many non-profits have scaled up from zero to $50m in revenue over the past 40 years?" Mr Bannick says. "The answer, according to a study by Bridgespan, a non-profit adviser, is 142. How many for-profits have done so? It is tens of thousands. If their product or service is contributing to the good of the world, they can have a more significant positive impact."
The emergence of these multi-pronged approaches to using a $1 billion fortune have changed what it means to consider oneself a philanthropist. Making a donation and having a library named after you pales against the ambition of a new generation of givers.
The success of this evolution will be measured not only by the diseases cured, the lives saved or improved and the social challenges overcome, but also in part by the acceptance of this approach among the public at large.
For now, there are some sceptics. Jesse Eisinger of ProPublica, the investigative journalism outfit founded by subprime mortgage billionaires Marion and Herbert Sandler, tweeted after Mr Zuckerberg's pledge this month: "I'm so grateful to Silicon Valley for having disrupted my definition of philanthropy."