An engine is provided for displaying an application for hosting a second application. The hosting application can be a sidebar on a display. The engine can contain a part or program which can include a manifest file, a definition file and/or a script file. The manifest file may contain a pointer to at least one of the definition file and the script file. The engine may also contain a loader that can locate the definition file and/or script file (e.g., via pointers in the manifest file) and load the definition file and/or script files of the part for processing. The engine may also execute script associated with the part and convert an object model into a user interface which can be displayed at a predetermined location on a display or docked onto a sidebar. The user interface can further be manipulated or relocated within the sidebar or removed (i.e., undocked) from the sidebar. The sidebar may be exploded or imploded with the corresponding parts on the sidebar displayed on the desktop or another application (exploded) or returned to the sidebar (imploded).