“Find your abundance mindset. Give away or ask for anything you want.” This is the inspiring, sweeping slogan of the Buy Nothing Project, an online community committed to exchanging free stuff among local people that was founded in 2013. A few decades into the internet era, the distribution of our excess resources online is a familiar concept: A similar platform, the Freecycle Network was founded a decade earlier in 2003; Gumtree, Craigslist and Facebook Marketplace are all full of people off-loading their unwanted possessions.

The Buy Nothing Project built on these concepts, but its founders, Liesl Clark and Rebecca Rockefeller, had loftier ideals: not only to be a means of exchanging goods, but to be a hyperlocal social movement that would ultimately create stronger bonds and encourag...