ToscaWidgets is a system for creating re-usable web components, such as a popup calendar or a rich text editor. In general, components consist of an HTML template, static resources (JavaScript, CSS, Images, etc.) and server-side code. ToscaWidgets allow these to be packaged into a “widget”, that a web developer can then easily use in their application.
In practice, the main use for widgets is for generating forms, and this functionality is in a separate package, tw.forms. There are also a number of separate widget libraries, for a variety of uses.