An APL-based high-productivity software--de-vel-op-ment environment is shown to enable small teams of two or three persons to build complex engineering software systems. The productivity and flexibility of such small teams, equipped with this environment, enables them to build customized engineering application systems economically. These customized systems are far more useful for the particular applications they address than are the generic systems that are commonly produced by large software-development groups. A customized engineering application system is described, illustrating the productivity of the two APL2-based computer-aided software engineering (CASE) tools used for its implementation and long-term software maintenance. The system is presented in some detail, to demonstrate its sophistication and thus provide a measure of the productivity of the software-development environment. The two CASE tools that comprise this software-development environment are used to build interactive graphical application systems, and to build systems for applications that require or can benefit from distributed cooperative processing. A list of some customized application systems built using the described environment is provided, along with estimates of the implementation efforts. The features of APL2 that play a key role in the effectiveness of these tools are also discussed.