User interface toolkits and higher-level tools built on top of them play an ever increasing part in developing graphical user interfaces. This paper describes the XIT system, a user interface development tool for the X Window System, based on Common Lisp, comprising user interface toolkits as well as high-level interactive tools organized into a layered architecture. We especially focus on the object-oriented design of the lower-level toolkits and show how advanced features for describing automatic screen layout, visual feedback, application links, complex interaction, and dialog control, usually not included in traditional user interface toolkits, are integrated.

TRACK is a kit to interactively construct environments that trace the execution of methods and the flow of messages between SMALLTALK-80 objects. It enables the user to set up traces by means of direct manipulation. This is done by placing obstacles between icons representing specific classes and instances much in the way a jumping course is set up. TRACK may be used to generate multiple visualizations of programs which may be concurrently run. It is a browsing and debugging tool as well as an algorithm animation tool. TRACK is tightly integrated with the standard tools of the SMALL- TALK-80 programming environment.