Maybe you already heard of the cwrap project. A set of tools to create a fully isolated network environment to test client/server components on a single host. socket_wrapper is a part of cwrap and I released version 1.1.0 today. In this release I worked together with Michael Adam and we implemented some nice new features like support for IP_PKTINFO for binding on UDP sockets, bindresvport() and more socket options via getsockopt(). This was mostly needed to be able to create a test environment for MIT Kerberos.
The upcoming features for the next version are support for passing file description between processes using a unix domain socket and sendmsg()/recvmsg() (SCM_RIGHTS). We would also like to make socket_wrapper thread-safe.