Open source implementation of Simple Sharing Extensions (SSE) is available now!
SSE is an XML micro-format and corresponding sync algorithm that can be embedded in RSS or Atom feeds to allow for two-way synchronization among peers. More important: the algorithm allows for mesh-style synchronization between nodes, with no concept of a "master" copy. This can be game-changing for data-exchange and app-level data interop. But only the future will tell....