The D-Bus Broker project
The D-Bus Broker Project is an effort to rethink the D-Bus message bus andproduce an implementation that addresses many of its longstanding problems;this project has now made its first public release. "Its aim is toprovide high performance and reliability, while keeping compatibility tothe D-Bus reference implementation. It is exclusively written for linuxsystems, and makes use of many modern features provided by recent linuxkernel releases." See thispost for an introduction to the project, or the GitHub page forsource. This is a purely user-space implementation.