Traditional transaction models ensure robustness for distributed applications through the properties of view and failure atomicity. It has generally been felt that such atomicity properties are restrictive for a wide range of application domains; this is particularly true for robust, collaborative applications because such applications have concurrent components that are inherently long-lived and that cooperate. Recent advances in extended transaction models can be exploited to structure long-lived and cooperative computations. Applications can use a combination of such models to achieve the desired degree of robustness; hence, we develop a system which can support a number of flexible transaction models, with correctness semantics that extend or relax serializability. We analyze two concrete CSCW applications - collaborative editor and meeting scheduler. We show how a combination of two extended transaction models, that promote split and cooperating actions, facilitates robust implementations of these collaborative applications. Thus, we conclude that a system that implements multiple transaction models provides flexible support for building robust, collaborative applications.