This paper introduces COAST, an object-oriented toolkit for the development of synchronous groupware, which enhances the usability and simplifies the development of such applications.COAST offers basic and generic components for the design of synchronous groupware and is complemented by a methodology for groupware development.Basic features of the toolkit include transaction-controlled access to replicated shared objects, transparent replication management, and a filly optimistic concurrency control.Development support is provided by a session concept supporting the flexible coupling of shared objects' aspects between concurrent users and by a fully transparent updating concept for displays which is based on declarative programming.