The state of the art in (computer-assisted) project management is based on the assumption that it is possible to isolate knowledge concerning project management from competence concerning the subject of the project. There are various software tools to support project management functions. However, investigating some consulting projects, a particular type of projects, reveals that this limitation hinders its application. Thus, we subdivide project management knowledge into three classes: universal project management knowledge, knowledge about the organisation which performs the project, and knowledge about the project class of which the actual project is a member. Based on these abstractions, a three layer architecture of project management support software is developed. Rule-based systems are advantageous to maintain knowledge which changes frequently over time. That is, in our case, the knowledge about the organization and, even furthermore, the knowledge about the project class. However, these components are not applicable universally. So, the development costs of project management support software increase with the number of organizations and the number of project classes. A prototype of these concepts has been implemented for a consulting company.