Moccasin looks very interesting for Taskboard.  Move, resize, and undo are built into the framework:

Excerpted from this description by the author of moccasin, Joe Berkovitz:

Moccasin is not a “thin” framework that encapsulates a set of recommended practices like Cairngorm. It’s more of a “thick” framework. Moccasin is aimed at building a particular type of app: one with interactive graphical views that support a lot of mouse gestures, have some notion of compound or nested views, have some notion of a current selection, a clipboard for cut/copy/paste, need robust undo/redo, and must load and save documents to persist the editor state. The views in question are generally not Flex UIComponents in Canvases or Boxes, but lower-level Flash DisplayObjects that can have very arbitrary shapes and layout geometries. Within this domain, Moccasin very much adheres to an MVCS way of thinking: there is a model representing the edited document’s state, a set of views that adjust to the model’s state via events, a controller which changes the model in response to user actions, and a set of services responsible for talking to the world around and outside the application.

Joe Berkovitz is the same guy that wrote the article introducing the MVCS blueprint and is also behind the really cool music notation program Noteflight.