This paper presents similarity in the design and the implementation of a Computer Aided Software Engineering (CASE) tool on three platforms. OODesigner is a tool that was initially developed to support Object Modeling Technique (OMT). An initial Unix version has been developed since 1994. In 1997, after the completion of the Unix version, we began developing a Java version and a Windows version to support Unified Modeling Language (UML). The development of a CASE tool is a typical application of the Model-View-Controller (MVC) paradigm. Thus, we obtained a common design pattern among the versions in the MVC point of views. This design similarity can be used to develop several kinds of CASE tools with the corresponding design notations. In this paper, we present the process we followed to develop the three versions and we discuss the similarity found among them. We also outline a kind of generic architecture for the design and the implementation of CASE tools.