We assume you are familiar with terms such as superimposed information, mark, and context.

A superimposed application is any application that incorporates marks in its information model. Superimposed application designers are free to choose any information model and user interface model based--they only need to include the ID (a string value) of each mark used in their information model. The application will need to initiate one or more of the operations on marks. It may retrieve none, some, or all of the context elements defined for marks.

Sidepad

Mash-o-matic

SISRS: The Superimposed Scholarly Review System (White Paper)

SIMPEL: A superimposed application being developed by some students at Virginia Tech

RIDPad and Schematics Browser: Early SPARCE applications