Pastry is a peer-to-peer system that was developed in the 2000’s. One of the primary researchers was Miguel Castro, who interestingly was my TA when I took 6.170 as an undergrad back at MIT!
I gave a talk on Pastry in 2018 at the Boston–Cambridge chapter of Papers We Love.
FreePastry was an early open-source implementation in Java. I personally find it a bit hard to grok the codebase, since it suffers from many of the overengineering patterns that often plague a Java project. But it's still useful to compare against the papers when you can find the good bits!
The FreePastry website also has a good bibliography of Pastry-related academic papers. It cuts off in 2005. Is that because no further work was done on Pastry? Or because the FreePastry project went stale?