GNUnet is an amazing framework for pseudonymous distributed applications being developed at INRIA and the Munich University of Technology. The secushare project is exploring how PSYC behaves on top of GNUnet. See PSYC2 for details.
You can think of GNUnet being for distributed apps what openssl is for federation: The common building block necessary to get all kinds of applications deployed. With something such as GNUnet commonplace on all computers and devices, distributed apps can become as ubiquitous and multifaceted as client/server and web-based computing is today.
GNUnet is written in C.
Available in the GNUnet SVN repository:
svn checkout https://gnunet.org/svn/gnunet
git svn clone https://gnunet.org/svn/gnunet
2 See also
More thoughts on GNUnet on the page for pseudonymous infrastructures.