Our work addresses the needs of multiple information workers collaborating on joint projects, which typically require finding, analyzing, and synthesizing information from heterogeneous sources. We report on iterative design, implementation, and assessment of collaborative tools for sensemaking tasks. Our goal is flexible, lightweight tools that both facilitate the activities done individually and lower the costs of effective collaboration. We suggest several approaches to enhance such collaborative sensemaking tools. These approaches include explicit representation of multiple team activities, integrated support for synchronous communication, and views of collected information that are tuned to both the reading and organizing phases of sensemaking. We present an integrated pair of tools, ContextBar and ContextBook, which illustrate these approaches, and describe the results from a formative evaluation of these tools.