Embodiments of the present invention are directed to composite applications that can be created and implemented using components of a platform disclosed herein. Widgets associated with one or more products available in a mashup container can be implemented based on a selection by a user of the widgets from a widget catalog. A behavior of, and an interaction between, the widgets can be defined using metadata data associated with the widgets without requiring assistance from the user. A skin can be applied to the composite application that controls a visual presentation of the application on a display.