Abstract: TRACY is a prototype of a middleware architecture that supports the migration of agents (in our definition: self contained, autonomous objects) in heterogeneous networks with the aim to complement more traditional distributed architectures. TRACY supports a weak form of (optimized) agent migration in a network of agent servers and implements local message passing between agents. Derived from a concise evaluation of requirements, mostly targeted towards eCommerce and intranet applications, TRACY is based on a three layer architecture model that supports a clean separation of concerns. A fully functional prototype of TRACY is by now ready for a first release and will be offered to system developers on the basis of an open-source venture. Currently, we are developing an industrial strength reference installation with a partner in the transport and logistics domain. The focus of this paper are the lessons learned during requirements analysis and system design, and the architecture of TRACY.