Real-time Collaborative Software Engineering (CSE) tools have many perceived benefits including increased programmer communication and faster resolution of development conflicts. Demand and support for such tools is rapidly increasing, but the cost of developing such tools is prohibitively expensive. We have developed an architecture, CAISE, to support the rapid development of CSE tools. It is envisaged that the architecture will facilitate the creation of a range of tools, allowing the perceived benefits of collaboration to be fully realised. In this paper, we focus on the development of CSE tools within the CAISE architecture. We present examples to illustrate how such tools are constructed and how they support realtime multi-user collaborative software development. We also address issues related to the number of collaborators and discuss performance aspects.