CASA (Collaborative Agent System Architecture) is an agent development platform that aims to support flexible development of societies of agents such that researchers and others can experiment with various agent communication protocols and social organization. The flexibility described here is multi-facited. At the intra-agent level, developers must be able to implement the inner workings of their agents in a variety of ways to implement specific behaviours. At the social (inter-agent) level, developers must be able to describe social norms among agents at a global scale, independent of individual agents. In addition, CASA endeavors to offer basic communication services, messaging services, commandline services, and plug-in logics and ontologies. All this flexibility can lead to an unwieldy system that could be difficult to use, so the flexibility must be carefully balanced against ease-of-use, both for the developer and the end-user of the agent systems.