[incr Tcl] is a set of extensions to the Tcl language for object-oriented programming. [incr Tcl] (itcl) provides the extra language support needed to build large Tcl/Tk applications. It introduces the notion of objects, which act as building blocks for an application. Each object is a bag of data with a set of procedures or "methods" that are used to manipulate it. Objects are organized into "classes" with identical characteristics, and classes can inherit functionality from one another.
Tk Drag and Drop is an extension for Tcl/Tk to add native drag and drop capabilities to the Tk toolkit. It is designed for Tk versions 8.3.3 and higher. Native drag and drop are supported under Microsoft Windows (XP, Vista, 7), Mac OS X Leopard (Cocoa framework), and Linux (XDND, drag support missing).