 The Horus project was originally launched as an effort to redesign  the <A HREF="http://www.cs.cornell.edu/Info/Projects/ISIS">Isis</A> group communication system, but has evolved into a general purpose communication architecture with advanced support for the development of robust distributed systems in settings for which Isis was unsuitable, such as applications that have special security or real-time requirements. Besides the practical uses of our software, the project has contributed  towards the theory of <EM>virtually synchrony</EM>, a runtime model used for our implementation of data replication and fault-tolerance.   At the same time, our software is much faster and lighter weight than the Isis system. <P>
