This paper describes the design of a distributed system built using Java that supports peer-to-peer communication among processes spread across a network. We identify the requirements of a software layer that supports distributed computing, and we propose a design that meets those requirements. Our primary concerns are (I) the identification, specification, and implementation of software components that can be composed in different ways to develop correct distributed applications; (2) reasoning about the components systematically; and (3) providing services to the components. This paper deals with the last of these concerns. Though our implementation uses Java, the fundamental ideas apply to any object-oriented language that supports messaging and threads. Alternative implementations use such languages coupled with object request brokers or remote procedure invocation mechanisms.