Activity-Based Computing (ABC) has been proposed as an organisational structure for local desktop management and knowledge work. Knowledge work, however, typically occurs in partially overlapping subgroups and involves the use of multiple devices. We introduce co-Activity Manager, an ABC approach that (i) supports activity sharing for multiple collaborative contexts, (ii) includes collaborative tools into the activity abstraction and (iii) supports multiple devices by seamlessly integrated cloud support for documents and activity storage. Our 14 day field deployment in a multidisciplinary software development team showed that activity sharing is used as a starting point for long-term collaboration while integrated communication tools and cloud support are used extensively during the collaborative activities. The study also showed that activities are used in different ways ranging from project descriptions to to-do lists, thereby confirming that a document-driven activity roaming model seems to be a good match for collaborative knowledge work