In this paper we present Malai, a model-based user interface development environment. Malai is dedicated to the conception of post-WIMP (Window, Icon, Menu, Pointing device) interactive systems. Malai aims at gathering together principles from Norman’s action model, instrumental interaction, direct manipulation, the interactor concept and the DPI model (Documents, Presentations, Instruments). It completes works on data manipulation techniques used to link source data to user interfaces. We show how Malai can improve modularity and usability of interactive systems by considering actions, interactions and instruments as reusable first-class objects. Malai has been successfully used for the development of several post-WIMP interactive systems. We introduce each Malai component using the same example: a vector graphics editor.