In this paper, we describe the design and implementation of a middleware system named Possession System. The system is designed based on Possession Model which provides users with a consistent view of application components, networked sensors, distributed devices by introducing two separated abstractions: Body and Soul. Possession System realizes a simple framework to deal with the adaptation of distributed multiuser applications by changing relations among Bodies and Souls. Furthermore, it enables users to interact with system components with a simple operation named possession. Distributed multiuser applications built on top of our middleware realize adaptive behavior, which is achieved by a mechanism combining system events with various behavioral changes of application components including the migration of components. The middleware is applicable to adaptive systems in mobile and ubiquitous computing environment where unpredictable changes in available computing resources, device configuration, and geographic location frequently occur. We describe how multiuser applications using our middleware adaptively behave.