Workflow management systems (WfMSs) are accepted worldwide due to their ability of modeling and controlling business processes. In the past, we defined an intra-organizational workflow specification model, Process LANguage PLAN. PLAN, with the associated tools, allows user to describe the graph specification for porcesses, artifacts and participants' organization. PLAN has been successfully implemented in Agentflow and run with workflow (Agentflow) applications. PLAN and most current WfMSs adopt the centralized architecture in an organization, so that they can be applied in an organization only. The participants in different organizations cannot serve one another with workflows. In this paper, we present an inter-organizational workflow model, Collaborative Agentflow Process LANguage. CA-PLAN, extended from PLAN, let workflow systems inside an organization be specified as workflow services provided by the organization. Its inter-organizational architecture make user specify work applications as in PLAN. Besides, the related service techniques and supporting tools provided in Agentflow systems are presented.