Retroshare is F2F (darknet) network. But Freenet and GNUnet provide generic anonymous networking (with efficient caching!), without you setting up contacts with your peers beforehand. Network where you can access only preknown resources isn't that useful after all. At least for finding new peers. Think about web browser, if you could only open pages which urls you already know. Who needs Google for anything? With retroshare all resources are gone if you delete those, with Freenet & GNUnet you simply can't delete anything. Very different design. Plz read white and design papers.

Also see: http://secushare.org/